Are you using the same version of backup manager because the version you used before might have a different location of storing in the games and the current one will have a different location so it will be looking in the wrong place.
Different BM's uses different folders to store the game files in. If you switch from one Bm to another, you might want to copy the games into a folder which the alternate BM recognises. Below are folders to look for your game files.
Deleting the original BM also removes your game backup files. This has been rectified other BM's and versions and it seems as if the BM coders will now standardise backups to dev_hdd0/GAMES ... at least I hope so!
Credit to marc2590 (thanks) for the following on another post:
It depends on which version of Backup manager you used:
the original one used:
also check in:
the games will appear as BCUSxxxxx, BLESxxxxx, or BLUSxxxxx