Hi Mauro,
make sure the Removable Storage service is stopped and disabled...it doesn't work really well with BE.
Open up Backup Exec and go into Devices. Right-click your server, and choose the option to Pause your server. Give it 1 minute, unpause it and then try again.
Should this not work, run the Backup Exec Device Configuration Wizard and install the device drivers.
And finally...if the above doesn't work, completely uninstall the device:
1. Turn off the backup device, and remove it from Backup Exec and Device Manager.
2. If it has a SCSI cable, disconnect the cable from the server, and then shut the server down.
3. Restart the server. Verify that the device doesn't show up in Windows Device Manager, or Devices in Backup Exec.
4. Once done, shut down the server, and reconnect the device if necessary. Turn on, and allow it to run through the start-up procedure.
5. Check that it shows up in Device Manager & Devices...
6. Try running an Inventory job, followed by a backup.
Post the results here...