I had the lock up upon wake up from sleep with login screen issue... i cant' remember what i did to fix it.. i think it had something to do with sleeping shortly after the screen saver popped up.. i did a lot of tests and as soon as i seperated the time between sleeping and screen saver turning on it stopped... so try making sure they are about 5 minutes apart... mine typically did it after closing the lid.. i don't recall having it happen when it automatically when to sleep ... it's weird.. do a search for powerbook coma on the apple tech help site thingie.. there's a whole thread or ... eight.. on it lol