Marcelo - Use Query PRocess and Query SEssion Format=Detailed to see if the tape/drive is actually in use, and Query Request to see if an associated tape is needed.
A situation which goes on for days, as you have encountered, is abnormal, and may indicate that a tape mount is actually not completing, and that can be due to a drive defect or even a tape already in the drive (stuck there, after a previous dismount failed). Inspect the drive for problems. Depending upon your drive type, a Reset or power cycle may clear its condition. But thereafter keep an eye on the drive for further problems, where a technician would have to work on it. Richard Sims