Making Very Hidden Tabs Visible

I am trying open very hidden tabs in a spreadsheet that someone else has sent me.

In the VBA screen, I've tried just selecting the tabs to be visible but get the following error message.

"Unable to set the Visible property of the Worksheet class".

I've also tried running the following code but still doesn't appear to work.

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Does anyone have any suggestions? Under "File", it does say that "A password is required to open this workbook" so not sure if that's related.

Thanks.

Nothing is wrong with the code, so yes, there is a password.

Yes, that would prevent you from unhiding a sheet also.