Just over this last few days my iMac's acquired a rather nasty habbit of waking straight back up from sleep. This means that sometimes I can have to try 2 or 3 times before the cursed machine will actually sleep properly. Any ideas?
Well, test it all the same. Sometimes a flat battery in a Bluetooth Keyboard or Mouse can wake my iMac up. Turn them off (or unplug them if they're wired) before putting your Mac to sleep. Does it still need multiple attempts?