I think I happened on a bug in Sentinel 2.02.01. If you go through the motions to update scanner firmware, you get a pop-up window that says your firmware is up to date. If you miss clicking the OK button or the X in the upper right corner, that pop-up window goes away, but the underlying window showing progress of firmware checking remains. The only way to get out of Sentinel is to go to the Task Manager and stop it that way.
