Workaround to Event 57802 and 57804, catalog mistmatch (Following a successful upgrade, the Backup Exec Server Service fails to start and the event logs report an error "The Backup Exec Server Service detected a schema version mismatch)
1.- Upgrade existing BE 2010 R3 to 2012
2.- Using existing procedure, copy folders Catalog and Data to safe place or shared drive
3.- Install brand new Windows Server, with the EXACTLY same name as the old one, as on step 1.
4.- Copy the folders Catalog and Data from step 2.- using procedure accordingly
5.- Start services of the new BE 2012
6.- That's it!