Hi Ibrahim,
Try the following:
1. Ensure Removable Storage service is stopped, and disabled.
2. Open up Backup Exec, and delete the device.
3. Open up Device Manager in Windows, and delete the device from there too.
4. Disconnect the tape device/autoloader from the server, and power down the server.
5. Start up the server with the tape drive disconnected.
6. Open up Backup Exec and Device Manager, and verify the device doesn't show in there at all. If not (and it SHOULDN'T), shut down the server again.
7. Reconnect the tape drive/autoloader, and start it up...
8...and the start up the server about a minute afterwards.
9. Open up BE, and run the Device COnfiguration Wizard, and install the drivers for the tape drive.
10. Verify that it's now working.
This is to delete the device completely and redetect it, which is sometimes the only way.