Hmm, do you happen to have a spare e-mail address the turns could be sent to? It happened to me a time or two that my turn didn't get through for not apparent reason at all, and also a couple of times to other players when I was adminning a game. In each case just changing the address the turns were sent to solved the problem. Going back to the original address a few turns down the line also worked fine every time.
Of course, if anyone who actually knows something about his computers has a real solution instead of a workaround I'm all ears.
Edit: The first obvious answer is of course checking if you changed anything about your firewalls, spam filters, and whatnot.