I found this on Stack Overflow:
This is due some problem with references within VBA in your workbook.
In the VBA editor, go to 'Tools-> References'. There you would find a reference with 'MISSING:' in front. Uncheck that and your problem should be fixed.
If the missing reference was something like 'Visual Basic for Application' or 'Microsoft Office Object library, you should look for a reference that has no 'MISSING:' text and select this.
You find this in Tools>Macros>Visual Basic Editor
this opens a VBA editor, click on VBAProject(7_series ...), password: austin
Now do Tools>References and follow the advice above from stack overflow.
Apperantly the "Mid" funcrion was not found?!?
Now it works for me!