There are two possible ways to resolve this issue
This behavior may occur because an Initialize operation has not been performed on the library.
To run an Initialize operation, perform the following:
1. Go to the Devices window in Symantec Backup Exec for Windows server (tm)
2. Right-click the IBM library
3. Select Initialize
After performing these steps, the slots that showed up as empty should then show up as unknown media, and at that point inventory operations should complete successfully
1. On the Backup Exec Console, slots are shown as empty even though the slots have tapes in them.
2. On the Robotic library Console, You can see the tapes
3. Select the Data Cartridges option on the left hand side
4. Select the tapes that should be reflected in the backup exec server , from the drop-down menu select Assign & Click Go
5. Select Windows under Logical Library & Click Next
6. Wait for the operation to complete
7. Go to the Backup Exec server & tapes will be displayed