I'm sure this is a dumb question, but have you changed your remote batteries to see if that is it? Also, sometimes just resetting the receiver fixes this problem if they aren't communicating. You just push and hold the power button on the receiver - after about 5 seconds it will go off and then the receiver resets itself.
That being said... we've had to get new remotes a couple of times because they just flake out.
EDIT: one other thing to check is that you have the satellite button pushed at the top of the remote, instead of one of the others.