Word automation fails

[begizorrotz]

Years ago I wrote an application in VB.NET that opens Word documents to make certain corrections to them, and it has been running smoothly until now.
The code is as follows:

Imports Microsoft.Office.Interop.Word
...
Friend WithEvents oWord As Word.Application
Friend WithEvents oDoc As Document
Dim varMissing As Object = Type.Missing
...
oWord = CreateObject("Word.Application")
oWord.Visible = True
oDoc = oWord.Documents.Open(Main.docName.Text, varMissing, varMissing,
varMissing, varMissing, varMissing, varMissing, varMissing,
varMissing, varMissing, varMissing, varMissing, varMissing,
varMissing, varMissing, varMissing)
...

(Of course, I added Microsoft.Office.Interop.Word.dll reference)

Last July 13, coinciding with an automatic update of Word to version 16 (previously 15) the application stopped working, issuing the message:

"You cannot cast the COM object from type Microsoft.Office.Interop.Word.ApplicationClass to the interface type Microsoft.Office.Interop.Word._Application. An operation error occurred because the QueryInterface call on the COM component with IID {00020970-0000-0000-C000-0000000000046} generated the following error: The item was not found. (Exception from HRESULT: 0x002802B (TYPE_E_ELEMENTNOTFOUND))"

in the line of code "oWord.Visible=True".

I have verified in the Task Manager that before the error a "Microsoft Word" task has been created.

Does anyone have any idea why?

[#2 · Accepted solution]

This is not a solution, but...

I have proceeded to change the declarations of the variables, as follows:

Before:

Friend WithEvents oWord As Word.Application
Friend WithEvents oDoc As Document

Now:

Friend WithEvents oWord As Object
Friend WithEvents oDoc As Object

In the same way, I've modified the word and document application mapping code, as follows:

Before:

oWord = CreateObject("Word.Application")
oWord.Visible = True
oDoc = oWord.Documents.Open(Trim(Main.docName.Text), varMissing, varMissing,
varMissing, varMissing, varMissing, varMissing, varMissing,
varMissing, varMissing, varMissing, varMissing, varMissing,
varMissing, varMissing, varMissing)

Now:

oword = ctype(createobject("word.application"), microsoft.office.interop.word.application)
oDoc = CType(oWord.Documents.Open(Main.docName.Text, varMissing, varMissing,
varMissing, varMissing, varMissing, varMissing, varMissing,
varMissing, varMissing, varMissing, varMissing, varMissing,
varMissing, varMissing, varMissing), Microsoft.Office.Interop.Word.Document)

with the result that it works. But with the change I lost the ability to handle the "DocumentBeforeClose" event, which prevented the document from being closed outside the control of the application.

Additionally, the following code, (which previously did not produce any error)

rngParagraphs = oWord.ActiveDocument.Range(Start:=oWord.ActiveDocument.Paragraphs(1). Range.Start, End:=oWord.ActiveDocument.Paragraphs(oWord.ActiveDocument.Paragraphs.Count). Range.End)

causes the "Count is read-only" error.

But replacing it with:

Dim nParg As Single = oWord.ActiveDocument.Paragraphs.Count
rngParagraphs = oWord.ActiveDocument.Range(Start:=oWord.ActiveDocument.Paragraphs(1). Range.Start, End:=oWord.ActiveDocument.Paragraphs(nParg). Range.End)

or what is the same, substituting .Activedocument.Paragraphs.Count for a variable in which the content has previously been loaded, works perfectly, which perplexes me.

He said that this is not a solution, just a palliative with problems. But I wanted to close the consultation with some more information.