I have Win 7. I'm running FSX and am halfway through an IFR route when suddenly I cannot respond to ATC. They give me a new heading and altitude and try as I might, I cannot get a response to them. None of the answer choices appear in the ATC window. They keep asking if I've heard the instruction and then cancel IFR. I have to reload the Flight Plan and then a short time later, the ability to respond fails again. Is this a problem with a solution?Thanks,Luke