If the former is right, apply a combo update from Apple site. I might do the trick.
There are times when my iMac will wake from sleep for no apparent reason. Sometimes, several times a night. The glare from my screen often wakes me. If I get up and select Sleep again, it performs normally but may wake up again.
I have "Wake for Network Access" turned off, so that shouldn't be it.
Does anyone else have this problem? Any suggestions?