Symantec changed something in version 11d. I do not know what, but it caused corruption in Microsoft RSM database.
Many newsgroup posts have long winded and unanswered posts on the subject. Many suggest disabling Microsofts Removable Storage service, which is incorrect.
For me, the following fixed the problem.
1. Stop the Removable Storage Service, if started. Make sure it is set to Manual startup.
2. Stop the Backup Exec Services.
3. Go into C:WindowsSystem32ntmsdata folder, backup the contents of this folder.
4. Delete the files in this folder.
5. Start the Removable Storage Service and new files will be created.
6. Start the Backup Exec Services.
Now your drives should be seen in Backup Exec. It worked for me, I hope it works for you…. and saves you a load of time searching the web for an answer!