Hi 海波 史,
This is because in the past you must have some unfinished tasks which were running also when you restarted a box.
As you are running old version of NPrinting you do not have visibility what is currently running and was is finished.
I encourage you to upgrade to newer version of NPrinting where you can see which tasks are running whicha are finieshed and which failed... as well as kill/abort these tasks which did not go through.
On the other hand you are running unsupported environment (QlikVIew and NPrinting on one box are not supported) so many strange things can happen!