Sage 2020 Company Will Not Convert to 2021

SUGGESTED

I updated my Sage 50 server from 2020 to 2021, and converted all but one company just fine. I receive two errors:

Sage 2021 Conversion Error

and

Database Engine Unavailable

The problems are that no one is currently accessing the company I'm trying to convert, and that the Actian PSQL service is indeed running on the server. Has anyone encountered these errors before when trying to convert a company to a newer Sage version? Is there a lock file I need to delete prior to converting? It makes no sense to me how the other company files managed to convert just fine save for this one.