mac book air lion does not go to sleep when button pressed or lid closed

I'm struggling since a while with this tricky problem. 

I noticed yesterday that my battery was draining really fast and this was usually happening after the sleep period between work and gym then home.

My Mac was switching off the screen instead of sleeping. I cured it by going to System Preferences, then Sharing, and disabling network sharing options there.

NOTE Someone on forums mentioned resetting SMC & PRAM, fixing permissions, and disabling startup applications, but in my case none worked.

From time to time I experienced the same problem in a more transient and evident scenario (fan keeping spinning so the noise tells you that something is wrong with sleeping even if the screen goes black) and here is a way to check it:

1. Go to Utilities in the Applications folder and open the Terminal app.
2. Type "pmset -g" without the quotes and hit enter.
3. If "sleep" has 0 next to it and the words "imposed by" ; The number next to the imposed by is the process ID. Write that number down.
4. Type "ps -e" and hit enter. This will list all running processes.
5. Find the process imposing on the sleep mode and take appropriate action (kill -9 ID)

that's all for now Alex Barchiesi