During synchronization there are errors in DSA log and in Event Viewer, a migration session fails with the same error:
Common AcAdSwitches Error 0xe1000051. Cannot compare password hashes, source user: "username", target user: "username"
Error 0x80040111. ClassFactory cannot supply requested class
Damaged DSA instance
The error indicates an issue with the DSA itself.
As first troubleshooting step install a new DSA and specify a preferred DC and GC, migrate one user with password and ensure user has been migrated successfully. Then old DSA can be re-installed. When removing the old DSA it is very important to preserve (copy away) the folder UNDOSTORAGE, which is located in DSA directory.
Quest KB article SOL35842 has more details how to install a new DSA.