I agree with the other reply that Active Sync can be cranky, and also would recommend updating to 4.2. My phone is in and out of the USB cradle a dozen times a day, and half the time I get the "USB port not recognized. However when I absolutely positively have to get sync, I use the IR port on my 6700 to my laptop. It always works.
So far we haven't done Active Sync via Wireless so I can't address it.