Just for grins, shut down Backup Exec and rename the \catalogs folder to \catalogs.old .
restart BackupExec
try the Inventory and Catalog again
if this ever happens again, if you have a copy of BEDB.BAK to use, copy\restore the \catalogs folder to the new location before starting BackupExec for the first time (using NTBackup)
The BAK file should contain an entry for the tape volume, which enables BackupExec to access the catalog file associated with it.