Unrecoverable error working with session database

Have many older Capture One 12 Sessions. I have both C12 and CO22. These sessions will not open any longer and cannot be upgraded. This is the error: : "An error occurred and the session "19_ChicagoApril" must close. An unrecoverable error was encountered while working with the session's database. unable to open database. The session will now close."  I tried to upgrade and the upgrade failed, stating that the database could not be verified. Anyone encountered this? Recommendations.