A private subroutine in VBA is being activated by other workbooks -- Why?

Question

I have a private subroutine in Workbook A that is running any time I open or close and save other unrelated workbooks. I'm trying to understand why that occurs so I can capture all potential errors that may occur.

The subroutine is an ActiveX ComboBox named TabProg that is supposed to run when the value is changed. I have currently added in a check to see if the active sheet trying to run the code is the "Program Loading" sheet to try and divert any potential errors. See snippet below.

Private Sub TabProg_Change()
    MsgBox "Whomp!", vbOKOnly + vbExclamation
    If ActiveSheet.Name <> "Program Loading" Then  'do nothing
    Else
       'Run desired actions on "Program Loading" sheet
    End If
End Sub

Any known reasons why this is occurring or other ways to catch it would be helpful. Thanks!

Edit 1: I do not see this problem occur when I open other workbooks in new instances of Excel.

Edit 2: I have modified the code to include a message box whenever the code tries to run, now shown above. It is occurring every time I open or close and save any Excel file, including the file itself. The drop down list in the ActiveX ComboBox is a list of names that correspond to 10 sheets within Workbook A. If I delete the sheet that ComboBox is currently set to, the error will disappear. If I change the ComboBox to a different sheet, the error will reappear.

Answer 1

From what you've wrote in your question, I don't think that your problem can be replicated. I think that your Excel file got corrupted. I had an experience like this: had a file for experimenting with macros, one of the macros used Excel Speech object to say "This is a test file" on opening that particular file. The macro was (as all other macros from this file) not part of my PERSONAL workbook, it was assigned to ThisWorkbook in the bespoke file. At some point a funny thing happened: this "This is a test file" private subroutine got activated every time I opened any Excel file. I did not find any solutions, I just deleted the file where the subroutine was stored. This resolved the problem, but I have no explanation for this. I am afraid the same thing may apply to your file, but maybe other folks have a better idea... maybe it's something in the system registry??? I don't know. Can you manually copy elements / code from this file to a newly created file and just delete the original?