Hi,
I would suggest you to review the /Web/WebAppServer/SASServer1_1/logs/server.log log file, where you will be able to see the messages during start and stop time.
My initial guess is that this is "normal" just a timeout, and it will stop fine after some minutes, when some underlying threads will be completely stopped (possibly, user sessions, or other processes). But it is also possible that something else could be. ANyway, the clues will appear on this log file.