I'm running OS X and recently upgraded to Lion. Since then, every so often (maybe once every three days or so), my computer gets into a state where every app refuses to quit.
I can open new apps no problem, and all the open apps still work, but quitting them fails, including force quitting them. Usually, the Finder unexpectedly quits shortly thereafter, and the dock freezes sometime after that, followed by the menu bar sometimes.
Sometimes, windows stop losing key status, too (all remain highlighted with colored widgets). Usually, shutting down fails as well (because the open apps cancel logout).
Any idea where to start with this? I'm not even sure what could be causing this. I believe it's occurred with only Finder, Mail, iChat, iCal, and iTunes open.