I have been using ubuntu (natty 11.04) for a while now and just recently have been experiencing this problem with the screen auto-locking itself for no apparent reason. I have turned off the screen lock at all times, removed any timer associated with locking the screen and yet my screen continues to lock for no reason, even if I am in the middle of issuing some command (mouse click, key press..). Upon locking the screen the dialog box then appears asking for my password and one of two things happens: either the screen unlocks itself after a second with or without any input or it goes through the normal routine of authenticating the password and returning to the desktop. This happens at very sporadic and random times, half the time this error never occurs and the other half of the time it renders my machine nearly unusable, and it seems restarting does nothing to solve the problem. For the life of me I can't figure out why this keeps happening but it seems to have started after I installed the XBMC media player and switched it to use projectM as its visualizer, however whether that is anything more than a coincidence is beyond me. Has anybody else been experiencing this?