I had similar issue. I have bitdefender AV suite. I have disabled the bit defender firewall and enabled windows firewall. I am not 100% sure, but I think the firewall (bitdefender) was the main culprit. Hope this helps.
I'm experiencing exactly the same dis/reconnecting problem, and its quite frustrating. I dont know the cause of it either, but I do run BitDefender2011 as well so that might be a clue..