I'm not quite sure I understand what you are saying? When you say "but the channels 501 through 507 are not there", do you mean these channels are not in the receiver, or do you mean they are in the receiver but you get no picture? If it's no picture on the channels, you need to get a DC lock as already sugested. But, if the receiver doesn't have the channels stored, then you need to go to a channel that has the Maps and get the Maps reloaded into the receiver. Most of the Master Movie channels have these Maps and you can also get them from G1 channel 3. Go to G1 channel 3 and make sure you get a DC lock and then leave it off for about 30 minutes and check and see if you got the Maps. If not unplug the receiver for 15-30 seconds and when it reboots, leave it be for a few minutes and then check to see if you got the Maps? If you have a 920 receiver you will have to do the unplug/replug to get the Maps, but if you have a 922 you shouldn't have to do it that way? Good Luck!
Al
Also, you don't say what receiver you have. It has to be a 4dtv receiver to get these channels....