Can having multiple instances of Excel open cause VBA issues? - excel

Question

I have code in workbook A that opens and does stuff to workbook B. Code runs fine when workbook A and B are the only excel files open (or if workbook A is the only file open). However, if I open up any additional workbook (call it workbook C), the macro does not run correctly. It doesn't cause an error message, it just runs to completion without doing any of the "stuff" it's supposed to do (the stuff is basically finding things in workbook B and pasting them into workbook A).
FWIW, I have done the following simple experiment:
Open all 3 workbooks (A, B, & C)
select workbook C so that it is active and the front window
run the code workbookB.sheet1.activate (this is not verbatim, I know this code as written will fail)
When I do the above test, it doesn't even make workbook B the active workbook. Again, it doesn't cause excel to throw an error message, it just runs and leave workbook C as the active workbook.
Edit: I've tested more, the code below should change the value of a cell in workbook B, but instead is putting the value into workbook C. I am very confused, since workbook C is not referenced in any way (the module is in workbook A)
Sub test()
Dim wb As Workbook
Set wb = Workbooks.Open("U:\workbookB.xlsx")
wb.Worksheets("ED").Range("Z1").Value = "TEST"
End Sub
Edit 2: The issue was occurring when Workbook A and B had been open for several hours, and Workbook C was recently opened. I closed workbook B then re-ran the code and it is working correctly. This leading me to believe that there IS some sort of issue with multiple instances of excel opening. While this is hopefully low-risk, I am still curious if anyone has some way I could code around it as a precaution? Thanks!

Answer 1

There is a subtle bug (I hesitate to call it that, but that's what it looks like) you need to watch out for.
If the workbook you're trying to open via code is already open then occasionally you will see some unexpected behavior (such as the return value from Workbooks.Open() being assigned to ThisWorkbook instead of the file you expect).
For example the code below runs in "Tester.xlsm" and is opening "EmptyTest.xlsx", but if that file is already open, the Workbooks.Open call fails to correctly assign the wb variable, and it ends up pointing at "Tester.xlsm". That can cause problems.
To replicate,
open Excel
open "EmptyTest.xlsx"
open "Tester.xlsm"
run "Tester" sub
Test code:
Sub Tester()
Dim wb As Workbook
'with "EmptyTest" already open
Set wb = Workbooks.Open("C:\Tester\EmptyTest.xlsx")
Debug.Print wb.Name '>> Tester.xlsm - oops!
'close"EmptyTest" before proceeding
Workbooks("EmptyTest.xlsx").Close False
'with "EmptyTest" closed
Set wb = Workbooks.Open("C:\Tester\EmptyTest.xlsx")
Debug.Print wb.Name '>>EmptyTest.xlsx - OK
End Sub
Totally reproducible on my system (win10/Office 365)

Answer 2

I think your problem is that you are opening Workbook B. You state, if you close and re-open it then it works.
Therefore, any changes you have made to Workbook B will be lost as it will re-open the original workbook. (Auto Save does not actually save the workbook, it saves a separate copy.)
You need instead to check if the workbook is already open and only re-open it if it is not currently open.
(Very rough code)
Sub test()
Dim wb As Workbook
For Each wb In ThisWorkbook.Application.Workbooks
If wb.Path & "\" & wb.Name = "U:\workbookB.xlsx" Then Exit For
Next
If wb.Path & "\" & wb.Name <> "U:\workbookB.xlsx" Then Set wb = ThisWorkbook.Application.Workbooks.Open("U:\workbookB.xlsx")
wb.Worksheets("ED").Range("Z1").Value = "TEST"
End Sub
But (as others have said) you should really check that there are no other instances of Excel running and account for them also.