Claus,

No leading or trailing spaces, sheet is visible.

I did change the first line to

Private Sub Auto_Open

and the issue apparently went away. However, I'd really like to understand why this happened.

Art

On Tuesday, March 3, 2015 at 10:11:17 AM UTC-5, wrote:
I am running Excel 2010/Windows 7 on a large network. I've recently updated an application that was originally written 4+ years ago and has been enhanced throughout the years. The latest version works fine on my machine, but some users are getting the following error upon opening the macro:

Run-time error '32809'
Application-defined or object-defined error

The trigger is the following code in sheet 'ThisWorkbook'

Private Sub Workbook_Open()
Application.ScreenUpdating = False
Sheets("Instructions").Activate
Application.ScreenUpdating = True
End Sub

The error is pointing to the "Instructions" sheet (in this case it is also Sheet33

Any suggestions as to why this is happening?

Art