Symantec Backup Exec – Error “0xA000821 – Library Error – incompatible storage media detected in robotic library” occurs when an inventory is run against the robotic library

Last week, I encountered this situation:

• A Backup server with Windows 2003 and Symantec Backup Exec 12.5. The Daily Inventory Job has Error Reports with description: “incompatible storage media detected in robotic library”
• A Dell PowerVault TL4000 Tape library with two LTO3 drives, with a yellow “Media Alert” LED on. The Web interface showed me that some tapes has been marked “Bad”, so that explained the Media Alert.