My 2009 iMac with Lion keeps on getting stuck everytime my son's limited time ends and the computer subsequently wakes up from sleep.
How to reproduce
In other words, my son has a limited usage timetable set with parental controls. If he does not log out in time (e.g. if he forgets and walks off), I predictably find the Mac in an unusable state when it wakes up from sleep.
This is what I see
Instead of seeing a normal login screen, I see the login screen projected on a screen-size rotating cube. The cube rotates a few degrees and then gets stuck, then restarts, etc. The HD spins wildly. The mouse is the spinning rainbow wheel.
The only way out is to shut down by holding power off for 5 second (and I don't really like to do this while the HD is clearly very busy!).
What I have tried
I've googled to no avail: the most similar report I can find is this and has no solution.
This happened with Snow Leopard and also with Lion.
How do I prevent this?