I think that icon ties to outlook as well. Check to see that there are no messages in there requiring attention. I'm going to look for the regedit people used to use to fix this. Just to clarify, sliding to the messages tab on the slider, your screen says "no messages"?
If you still have it after this, you can try going
HERE and downloading fixunreadcount, but I'm using the cookie version so I can't test it.