Mine was doing this a few weeks ago....... and I have never figured out why, but if I had even spoken to anyone, it was throwing messages repeatedly, days later it would resend them and all kinds of funky shit....... so it isn't just you.
Had someone ask me what the hell I was talking about and resent me the message and it was a message I had sent him a month before..........
I re-installed and it was fine.
