"Method 'Calculation' of object '_Application' failed" error occurs on unpredictable attempts

The error "Method 'Calculation' of object '_Application' failed" is notoriously vague, but its intermittent nature is the biggest clue. It almost always points to a race condition or an unstable application state caused by how your code interacts with the Excel environment, especially when combined with userforms and screen updating.

I Think the error happens on this line: Application.Calculation = xlCalculationManual. You are trying to change a global application setting. The failure means Excel is in a state where it cannot process this request at that exact moment.

Here my solution approach with some Key Improvements (Replaced On Error Resume Next with a proper On Error GoTo ErrorHandler - The CleanExit block is now the only exit point, besides End Sub - The code now captures selectedRow = Selection.Row at the very beginning - The SetAppState helper sub makes the main code cleaner and less error-prone - The wait form is shown after the application state is set to "busy" - Using worksheet variables (wsProd, wsBkg) makes the code easier). Hope that Helps in your Projekt.

' Helper sub to manage application state
Private Sub SetAppState(ByVal isBusy As Boolean)
    Static originalCalculation As XlCalculation
    Static originalEvents As Boolean
    Static originalScreenUpdating As Boolean
    Static originalUpdateRemoteRefs As Boolean
    Static originalDisplayStatusBar As Boolean
    
    If isBusy Then
        ' Store original states first time
        If originalCalculation = 0 Then
            originalCalculation = Application.Calculation
            originalEvents = Application.EnableEvents
            originalScreenUpdating = Application.ScreenUpdating
            originalUpdateRemoteRefs = ActiveWorkbook.UpdateRemoteReferences
            originalDisplayStatusBar = Application.DisplayStatusBar
        End If
        
        ' Turn everything OFF for speed/stability
        On Error Resume Next ' Just in case calculation change fails
        Application.Calculation = xlCalculationManual
        Application.EnableEvents = False
        Application.ScreenUpdating = False
        ActiveWorkbook.UpdateRemoteReferences = False
        Application.DisplayStatusBar = False
        On Error GoTo 0
    Else
        ' Restore original states
        On Error Resume Next
        If originalCalculation <> 0 Then
            Application.Calculation = originalCalculation
            Application.EnableEvents = originalEvents
            Application.ScreenUpdating = originalScreenUpdating
            ActiveWorkbook.UpdateRemoteReferences = originalUpdateRemoteRefs
            Application.DisplayStatusBar = originalDisplayStatusBar
        Else
            ' Fallback to defaults
            Application.Calculation = xlCalculationAutomatic
            Application.EnableEvents = True
            Application.ScreenUpdating = True
            ActiveWorkbook.UpdateRemoteReferences = True
            Application.DisplayStatusBar = True
        End If
        On Error GoTo 0
        
        ' Reset stored states
        originalCalculation = 0
    End If
End Sub

Private Sub CommandButton2_Click() 'Save
    ' --- PREPARATION ---
    ' Declare all variables at the top
    Dim wsProd As Worksheet, wsBkg As Worksheet
    Dim rng As Range, cell As Range
    Dim first_DB_avail_row As Range
    Dim Highest_Version_Row As Long
    Dim existingVersions() As String
    Dim ver_find As Variant
    Dim ver_list As Object: Set ver_list = CreateObject("System.Collections.ArrayList")
    Dim padded_list As Object: Set padded_list = CreateObject("System.Collections.ArrayList")
    Dim v As Variant, parts As Variant
    Dim padded_v As String, leadChar As String, all_vers As String
    Dim i As Long 'Use Long instead of Integer for row counts
    Dim productID_To_Find As String
    Dim newVersionString As String
    Dim selectedRow As Long '*** CRITICAL: Store the selected row number explicitly ***
    Dim destRow As Range
    Dim srcDevRow As Range

    ' --- INITIAL SETUP & VALIDATION ---
    On Error GoTo ErrorHandler 'Use a proper error handler

    ' Set worksheet objects to avoid repeated lookups
    Set wsProd = ThisWorkbook.Sheets("Products")
    Set wsBkg = ThisWorkbook.Sheets("Background Data")

    ' *** CRITICAL FIX: Capture the active row BEFORE any UI changes ***
    If TypeName(Selection) <> "Range" Then
        MsgBox "Please select a product row first.", vbExclamation, "Business Manager"
        GoTo CleanExit
    End If
    
    selectedRow = Selection.Row
    If selectedRow < 4 Then 'Basic validation - assuming data starts at row 4
        MsgBox "Please select a valid product row (row 4 or greater).", vbExclamation, "Business Manager"
        GoTo CleanExit
    End If
    
    productID_To_Find = wsProd.Range("E" & selectedRow).Value
    
    If productID_To_Find = "" Then
        MsgBox "The selected row does not have a Product ID.", vbExclamation, "Business Manager"
        GoTo CleanExit
    End If
    
    newVersionString = stage_entry & Major & Minor & Patch

    'Handle first version case
    If Me.Caption = "First Version - Business Manager" Then
        If Me.ComboBox1.Value = "" Or Me.TextBox1.Value = "" Or _
           Me.TextBox2.Value = "" Or Me.TextBox3.Value = "" Then
            MsgBox "You must complete all fields.", vbExclamation, "Business Manager"
            GoTo CleanExit
        End If
        Insert_Product.ver_val = newVersionString
        Unload Me
        Insert_Product.new_product_ver_cancel = False
        GoTo CleanExit
    End If

    ' Validate entries for non-first version
    If Me.ComboBox1.Value = "" Or Me.TextBox1.Value = "" Or _
       Me.TextBox2.Value = "" Or Me.TextBox3.Value = "" Then
        MsgBox "You must complete all version fields.", vbExclamation, "Business Manager"
        GoTo CleanExit
    End If

    'Check for existing versions
    Call Find_Latest_Ver 'Get the current latest version
    If newVersionString = Highest_Version Then
        MsgBox "This version already exists (as the newest version).", vbExclamation, "Business Manager"
        GoTo CleanExit
    End If
    
    If Me.TextBox4.Value <> "" Then
        existingVersions = Split(Replace(Me.TextBox4.Value, vbCrLf, ""), "• ")
        For Each ver_find In existingVersions
            If Trim(ver_find) = newVersionString Then
                MsgBox "This version already exists.", vbExclamation, "Business Manager"
                GoTo CleanExit
            End If
        Next ver_find
    End If

    ' --- START LONG-RUNNING PROCESS ---
    Me.Hide 'Hide the form
    
    ' Set application state for performance/stability
    SetAppState True
    
    ' Show wait form modelessly
    PLZ_WAIT.Show vbModeless
    PLZ_WAIT.Label2.Caption = "Setting new version..."
    DoEvents

    ' --- CORE LOGIC ---
    ' Unprotect sheet
    wsProd.Unprotect Password:=wsBkg.Range("CY39").Value
    
    ' Pull data from the latest version
    Dim foundLatest As Boolean
    foundLatest = False
    Set rng = wsBkg.Range("E4:E7503")
    
    For Each cell In rng.Cells
        If cell.Value = productID_To_Find Then
            If cell.Offset(0, -2).Value = Highest_Version Then
                ' Copy values from the latest version's row to the selected row
                With wsProd.Rows(selectedRow)
                    .Cells(1, "B").Value = cell.Offset(0, -3).Value 'Name
                    .Cells(1, "C").Value = newVersionString 'Product Version
                    .Cells(1, "D").Value = cell.Offset(0, -1).Value 'File
                    .Cells(1, "E").Value = cell.Value 'ID Number
                    .Cells(1, "F").Value = cell.Offset(0, 1).Value 'Category
                    .Cells(1, "G").Value = cell.Offset(0, 2).Value 'Details (Description)
                    .Cells(1, "K").Value = cell.Offset(0, 6).Value 'Release Date
                    .Cells(1, "L").Value = cell.Offset(0, 7).Value 'Copyright Y/N button
                    .Cells(1, "M").Value = cell.Offset(0, 8).Value 'Copyright Status
                    .Cells(1, "N").Value = cell.Offset(0, 9).Value 'Year
                    .Cells(1, "O").Value = cell.Offset(0, 10).Value 'Copyright Statement
                    .Cells(1, "P").Value = cell.Offset(0, 11).Value 'Published Y/N button
                    .Cells(1, "Q").Value = cell.Offset(0, 12).Value 'Publish Status (Date)
                    .Cells(1, "R").Value = cell.Offset(0, 13).Value 'Web Link
                    .Cells(1, "S").Value = cell.Offset(0, 14).Value 'Withdraw Date
                End With
                Highest_Version_Row = cell.Row
                foundLatest = True
                Exit For
            End If
        End If
    Next cell

    If Not foundLatest Then
        MsgBox "Could not find the data for the latest version ('" & Highest_Version & "') to copy from.", vbCritical, "Error"
        GoTo ErrorHandler
    End If
    
    ' Save new version to version database
    Set first_DB_avail_row = wsBkg.Range("C7506").End(xlUp).Offset(1, 0)
    Set destRow = first_DB_avail_row.EntireRow
    
    ' Copy product data to database
    destRow.Cells(1, "B").Value = wsProd.Cells(selectedRow, "B").Value 'Name
    destRow.Cells(1, "C").Value = wsProd.Cells(selectedRow, "C").Value 'Product Version
    destRow.Cells(1, "D").Value = wsProd.Cells(selectedRow, "D").Value 'File
    destRow.Cells(1, "E").Value = wsProd.Cells(selectedRow, "E").Value 'ID Number
    destRow.Cells(1, "F").Value = wsProd.Cells(selectedRow, "F").Value 'Category
    destRow.Cells(1, "G").Value = wsProd.Cells(selectedRow, "G").Value 'Details (Description)
    destRow.Cells(1, "K").Value = wsProd.Cells(selectedRow, "K").Value 'Release Date
    destRow.Cells(1, "L").Value = wsProd.Cells(selectedRow, "L").Value 'Copyright Y/N button
    destRow.Cells(1, "M").Value = wsProd.Cells(selectedRow, "M").Value 'Copyright Status
    destRow.Cells(1, "N").Value = wsProd.Cells(selectedRow, "N").Value 'Year
    destRow.Cells(1, "O").Value = wsProd.Cells(selectedRow, "O").Value 'Copyright Statement
    destRow.Cells(1, "P").Value = wsProd.Cells(selectedRow, "P").Value 'Published Y/N button
    destRow.Cells(1, "Q").Value = wsProd.Cells(selectedRow, "Q").Value 'Publish Status (Date)
    destRow.Cells(1, "R").Value = wsProd.Cells(selectedRow, "R").Value 'Web Link
    destRow.Cells(1, "S").Value = wsProd.Cells(selectedRow, "S").Value 'Withdraw Date

    ' Copy Development Status Data from latest version
    Set srcDevRow = wsBkg.Rows(Highest_Version_Row)
    
    ' Use bulk copy for efficiency
    destRow.Cells(1, "T").Resize(1, 7).Value = srcDevRow.Cells(1, "T").Resize(1, 7).Value 'Title through Dev Log (1)
    destRow.Cells(1, "AA").Resize(1, 3).Value = srcDevRow.Cells(1, "AA").Resize(1, 3).Value 'Framework through Stage
    destRow.Cells(1, "DA").Resize(1, 7).Value = srcDevRow.Cells(1, "DA").Resize(1, 7).Value 'Dev Logs (2-7)
    destRow.Cells(1, "AD").Resize(1, 13).Value = srcDevRow.Cells(1, "AD").Resize(1, 13).Value 'Bugs through Customer Request

    ' --- VERSION LIST & VALIDATION ---
    ' Build version list
    ver_list.Add newVersionString
    For Each cell In rng.Cells
        If cell.Value = productID_To_Find Then
            ver_list.Add cell.Offset(0, -2).Value
        End If
    Next cell

    ' Sort versions with padding technique
    For i = 0 To ver_list.Count - 1
        v = ver_list(i)
        If Len(v) > 0 And Left(v, 1) Like "[A-Z]" And InStr(v, ".") > 0 Then
            leadChar = Left(v, 1)
            parts = Split(Mid(v, 2), ".")
            If UBound(parts) >= 2 Then
                padded_v = leadChar
                padded_v = padded_v & Right("000" & parts(0), 3)
                padded_v = padded_v & Right("000" & parts(1), 3)
                padded_v = padded_v & Right("000" & parts(2), 3)
                ver_list(i) = padded_v & "|" & v
            End If
        End If
    Next i

    ' Sort descending
    ver_list.Sort
    ver_list.Reverse
    
    ' Reconstruct version list
    For i = 0 To ver_list.Count - 1
        If InStr(ver_list(i), "|") > 0 Then
            ver_list(i) = Split(ver_list(i), "|")(1)
        End If
    Next i
    
    ' Create validation list string
    all_vers = "," & Join(ver_list.ToArray, ",")
    
    ' Apply validation to the version cell
    With wsProd.Cells(selectedRow, "C").Validation
        .Delete
        .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, _
             Operator:=xlBetween, Formula1:=all_vers
        .IgnoreBlank = True
        .InCellDropdown = True
        .InputTitle = ""
        .ErrorTitle = ""
        .InputMessage = ""
        .ErrorMessage = ""
        .ShowInput = False
        .ShowError = False
    End With
    
    ' Re-protect sheet
    wsProd.Protect Password:=wsBkg.Range("CY39").Value

    ' --- FINALIZATION ---
    Sheet2.UPDATE_DB_FORCE = True
    ' Pass the specific cell that changed
    Application.Run "Sheet2.Worksheet_Change", wsProd.Cells(selectedRow, "C")
    Sheet2.UPDATE_DB_FORCE = False
    
    MsgBox "New version '" & newVersionString & "' created successfully!", vbInformation, "Success"
    Unload Me

CleanExit:
    ' This section runs whether there's an error or not
    ' Restore application state
    SetAppState False
    
    ' Clean up UI
    On Error Resume Next
    Unload PLZ_WAIT
    On Error GoTo 0
    
    ' Release all object variables
    Set wsProd = Nothing
    Set wsBkg = Nothing
    Set rng = Nothing
    Set cell = Nothing
    Set first_DB_avail_row = Nothing
    Set destRow = Nothing
    Set srcDevRow = Nothing
    
    If Not ver_list Is Nothing Then
        ver_list.Clear
        Set ver_list = Nothing
    End If
    Set padded_list = Nothing
    
    Exit Sub 'Normal exit

ErrorHandler:
    ' This section only runs when an actual error occurs
    MsgBox "An unexpected error occurred:" & vbCrLf & _
           "Error #" & Err.Number & ": " & Err.Description & vbCrLf & _
           "The operation has been cancelled. Please try again.", vbCritical, "Business Manager"
    
    ' Jump to cleanup section to restore state
    Resume CleanExit
End Sub

The code is not Tested, save your file as a backup before.