At Quinnipiac, we have a classroom with Macs running OS Lion (10.7.5). We recevied complaints from the faculty that some of the stations could not print. Our Lab Coordinator investigated and tested (outside of class hours); all of the stations worked fine. For diagnosis, this person visted the class in session. She found that some of the stations could not print. Instead of displaying the Popup client, a message appeared stating that the Popup was unavailable. She found that each station that failed to print had multiple users logged in - if the Mac went to sleep during an inactive session, a login screen would appear and a subsequent user would log on without logging out the previous session.
We surmise that the earlier user session(s) took hold or ownership of the Popup process and would not either release it or allow another instance to be spawned.
Has anyone else come across this behavior? Our immediate solution is to have the Macs automatically reboot if an inactivity timer is exceeded. With all of the previous sessions cleared/closed, the Popup client works fine.