128T Error Hard Error failed to preform inventoy check

Check what other messages you are getting, they often yield a better idea about what's going on. It could be a picker failed to communicate, or picker couldn't move. If it's a move error, remove all tapes and make sure the carriers are properly seated in the drawers, then power up the unit and see if the error goes away. If so, it may have been a tape sticking out. If the error persists, the picker may be stuck. You can try to move the picker by hand a little bit to losen it (obviously with the power dosconnected), but if the issue persists, you may require service (probably replace the picker assembly).

we had this problem too... the first thing we went through was ensuring that the Firmware was up to date for both Library and tape. The Techo said that there was problem that can cause this that was fixed in the latest...

Of course, our problem went on to be a Tape that was dodgy and wasn't able to be lodaded.