Hi,
This might indicate a database issue. I have not seen an error message like this before, so I googled around, and found a few topics, here and here.
I am not entirely sure what this is, but it looks like a database file issue/corruption, that preventing table changes. The resolutions on those topics are to remove the table files via command line, as well as dropping them via the SQL app. I think you might have to contact your hosting provider about this. I do not recommend running any commands altering the database, unless you are experienced with it. Please always have database back-ups, before doing anything to the database.