command button suddenly does not function

I have created 2 command buttons for materials usage - the first button deletes rows with cell G=0,  sorts then subtotaled them; the second button - updates/refreshes the file.

After the first button is done - both buttons worked OK - as long as the view is not changed > but when the [2] at the upper left is clicked (to view the summarized data) - the first button just become dead! 

hope the following images can help analyze the problem.

many thanks

the first image is the main data

the second image is the result of sort/subtotal

the sub routines are as follows:

Private Sub CommandButton1_Click()  (deletes rows with G=0, sort then subtotal)

  Worksheets("MU").Activate
  Dim i As Long  (this deletes all rows with zero values for cell G)
  For i = Cells(Rows.Count, "G").End(xlUp).Row To 2 Step -1
  If Cells(i, "G") = 0 Then Rows(i).Delete
  Next i

  Range("A2:G206").Select
  ActiveWorkbook.Worksheets("MU").Sort.SortFields.Clear
  ActiveWorkbook.Worksheets("MU").Sort.SortFields.Add Key:=Range("A2:A206") _
  , SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:=xlSortNormal
  With ActiveWorkbook.Worksheets("MU").Sort
    .SetRange Range("A2:G206")
    .Header = xlGuess
    .MatchCase = False
    .Orientation = xlTopToBottom
    .SortMethod = xlPinYin
    .Apply
  End With
  Range("A1:G206").Select
  Selection.Subtotal GroupBy:=1, Function:=xlSum, TotalList:=Array(7), _  
  Replace:=True, PageBreaks:=False, SummaryBelowData:=True

  Dim LR As Long   (this fills up the unit of measure missing in the subtotal)
  LR = Range("C" & Rows.Count).End(xlUp).Offset(1).Row
  Range("C2:C" & LR).Select
  Selection.SpecialCells(xlCellTypeBlanks).Select
  Selection.FormulaR1C1 = "=R[-1]C"
End Sub

Private Sub CommandButton2_Click()  (this copies back the data from sheet "usage" back to sheet "MU")

  Worksheets("MU").Activate
  Cells.Select  
  Selection.RemoveSubtotal
  Sheets("usage").Range("A2:G555").Copy Sheets("MU").Range("A2")
End Sub