Look at the kernel log for likes that say "Wake reason =". You will see a code. Go to the following to find the meaning of the codes:
That may help shed light on why you machine is waking up.
If you cannot figure it out there's always utilities like PleaseSleep which try to force the system to obey the Energy Saver preferences.
Also, with respect to the Energy Saver preferences, make sure you don't have wake for network access checked.
Thanks for your reply, but as I stated above: Wake On Lan is OFF and there is no sign of "Wake reason" the only Error-like line is the:
kernel: Sound assertion "0 == fAudioEngineArray" failed in AppleHDADriver at line 3047 goto Exit
And Im not sure if I want to install 3rd party software to do the job that system tools should do. The whole thing started after the "No WIFI connection after waking up" update few days ago.
Thank you for the tip!
I got the same problem a few days ago, called Apple Support, spend an hour on the phone deleting .plist files, got transferred to a 'seniour consultant' who got me to re-install Lion, which fixed the problem for half-a-day.
After reading the printer story, I remembered that my 5-year old recently developed a facsination for hitting a print button whenever there is one, so I had to switch the printer off half-way through one of his 'print jobs'.
All I had to do now is to switch the printer on and let it go through to complete the queued printing, and the problem is gone!