Please copy&paste here the exact mt command line you used.
If there was an error message, please copy&paste it here too.
Knowing the type and model of the tape drive might be important too. If there was no error message at all, it might be a mechanical problem in the tape drive.
For example, we had a DDS tape with a loose label. The label had folded sticky-side-up and stuck to the "ceiling" of the tape slot, and the ejection mechanism did not have enough force to rip the label off and push the tape out completely.
When the ejection sequence completed, the tape drive detected that the tape was still pushed in and assumed that the user was pushing in a new tape, so it immediately loaded the tape again. The result: no error message, the tape just did not come out.
As I recall, that problem was solved by first using a good drive to review how exactly the ejection sequence *should* be working, then triggering the ejection sequence on the bad drive and switching the power off the drive at exactly the right moment. Then the tape was manually pulled out (very gently!) and the root cause (the loose label) was discovered & fixed.
The manuals for some tape drives may describe a manual emergency ejection procedure, to be used if the normal procedure does not work.
