Signal to check for this would be starting to see 196 errors or the next time you try to change you will not be able to load all the tapes you expect. You can open to see if you spot a tape.
You can try the following steps:
Press the eject button for 60 seconds. If this does not work you can try powering down the library (from the rear power sewitch) for 30 seconds.
Once the library is fully initialized open the door and hold the drive button for five seconds.
If these do not work call Service Express. If you are uncomfortable with attempting these steps call Service Express.
The i500 will send you a message stating that a tape is stuck. The suggested next step is to call Quantum regarding this error message.
Document compiled from information supplied by Bill Van Haften 7/20/2012