I think there is a bug where if a normal criminal turns insane it will inform you that they are eligible for parole, even though insane prinsoners are no longer eligible.

Then it will appear as if the que is jammed but actually the game functions normally otherwise. Once they are released, it should clear the label, still it's something to think about if playing with DLC enabled.

"Edit: Under Extras-Map Settings, you can turn off regular inmates turning insane"

This will help until they fix the bug.