I am sure your issue with sleeping could be from maybe the protector covering the prox. sensor on the front. possible to cut that area off, but I also know that I have had issues with older models of Samsung. when u put to sleep it wants to wake up. waiting to unlock and wont go out. it also could be a virus issue with an unofficial app you have, or maybe a issue with Samsung firmware. maybe someone else can chime in on this because that is about as far as I have gotten on it. my fascinate did it. my galaxy proclaim used to do it from time to time.
I was using unofficial batteries(acesoft) at the time I was getting the issues, have not seen the error on my proclaim since I have been official battery. so do u use official battery? this should narrow down the problem I hope bc I never found the cause either. Dell does a similar thing with laptops, use an unofficial charger, and it will refuse to charge the battery. same with the acesoft, that is y they give u a charge cradle with them.