I am not a sql expert like you, so I have different questions about your situation.
1 - I am assuming that the old catalog is still working in the old PSE version, and that it does not need to be 'repaired'
2 - The workaround I have suggested to create a new 'light' catalog db file may work as expected except for the impossibility to be converted (same error message) ?
We don't know the real source of the error message in your case or in the other conversation. It could be a programming error in the conversion module or an unexpected external config situation (hardware or software). Such errors are not likely to be recognized by 99% of the PSE users without an explicit error message; searching in the error log files is not common. Did you get an explicit message yourself?
Getting the attention of the Elements team requires that the bug be frequent enough and reproducible. Here it may be relatively frequent but hidden among the generic 'conversion failure' messages and anyway there is no clear suspicion between coding error or random config situation.