Backup Exec and Dell ML6000

We have a Dell ML6000 which Backup Exec (2012) connects to via a SAN on Windows 2008 Server R2. Unexpectedly the Backup Exec server does not see the library any more. No changes were made outside of replacing a bad drive. My question is - should Backup Exec be using the generic 'unknown media changer' within windows, or should it be using its own driver? It doesn't show up in Device Manger, and using tapeinst.exe doesn't seem to do anything other than see the two LTO drives. Thanks for any info in advance!