Get an error message when I try to unprotect a sheet using VBA. Why?

[OldManExcellor]

I have protected a sheet using:

Please Login or Register  to view this content.

When I click a button that runs the following macro, it works:

Please Login or Register  to view this content.

When I make a worksheet change which triggers the following sequence:

Please Login or Register  to view this content.

Then I get the attached error message on the line Sheet1.Unprotect. I tried adding Application.DisplayAlerts = False before unprotecting. But then the macro stopped already on Application.DisplayAlerts = False and the popup appeared. If I tell the macro to continue, it continues and finishes successfully despite the popup.

Why does this popup appear?
Run time error.png

PS. I can't upload the workbook as is because it contains lot's of company data. If I remove everything from the workbook, I don't get an error message any more when running the exact same macro. I don't know why.

[olle3770]

Do you have a global variable named sheet1 that refers to Worksheets(1)?

[OldManExcellor]

No, sheet1 is the codename of the protected sheet.

[OldManExcellor]

I have found that if execute

Application.GenerateTableRefs = xlGenerateTableRefA1

before I run the unprotect makro, it works.

WHY is it like this? I am pulling my hair.