Dude I had this problem last week....fawk it's SO frustrating!
I tried EVERYTHING...but in the end I had to hard reset, then it started working perfectly again.
Try going to activesync on your phone and disabling advanced network functionality. I don't think it will work for you, but you might as well try if you haven't already. Like I said, I was so pissed...I gave up hope and hard reset, without expecting it to work, but it did, so 'sall good now
