Ubuntu log out error

sometimes if I leave MuseScore running in the background
and have Jack running playing back mp3's with VLC
I sometimes experience an overall slowdown
after a couple of hours

e.g. cursor feels sluggish and the laptop fan is on high
I shut down all my apps and try to log out
I get an error message saying:

'/usr/bin/mscore.real
is not responding'

once I reboot everything seems OK

any other Ubuntu users out there experience this?