If the BKF files or IMG folders are encrypted then nothing we can do about those and those contents of those Backup Sets will not be recoverable.
You do have to install Backup Exec to read a BKF.
If the Backup Exec installation is encrypted (or part encypted) I would try a repair but expect to possibly have to do an uninstall re-install.
Before doing an uninstall though.
If you can confirm if the BEDB (either BEDB.BAK or the MDF, LDF pair of fiels) are not encrypted those might be useful so copy them away.
Similarly if you can confirm if the catalog fiels are encypted those might be handy to be copied as well.
Note if you are not sure if this server is clean you might want to consider a server rebuild just to be safe.