This is for the same message in proSeries, but it might help with FAM too.
https://accountants.intuit.com/support/en-us/help-article/save-data-file/file-currently-locked-anoth...
I put this into Google and the AI answer that appeared at the top might have some good ideas
fixed asset manager locked by other user
♪♫•*¨*•.¸¸♥Lisa♥¸¸.•*¨*•♫♪
