Usually this error message occurs after something has interrupted the connection between Sage 50 and its data.  Since the issue is occurring frequently when you try to close Sage 50, it may take some work to resolve.  I would start by manually restarting Actian using the steps in Section 3 (III) of this article: https://support.na.sage.com/selfservice/viewdocument.do?noCount=true&externalId=11613

Restarting Actian will resolve a lot of errors in Sage 50, but if the error comes back, you may need to work through some of the later sections in the article (4-7).

The good news is these should not affect your data or access to your company, though if you have to go all the way to the last section to resolve the issue, renaming the Userpref.dat file will reset all your user preferences.