try changing the address on the 21.0 and 4.0 to an odd number. The 21.0 does pro band A for odd numbers and pro band B for even. The 4.0 can only do pro band A, so if they're both on the same odd number, should work.zookeeper said:John, I have similar setup. When I set the 222k up both primary and secondary remote addresses were on 1. I took the 21.0 remote and went through the process of changing the remote address for the # 2 receiver to 2 and the screen shows the # 2 receiver address at 2 UHF Pro band B. I have heard about band a and band b but I don't know how to change to either one. My old 3.0 remote works with the #1 reciever but when I take my 4.0 remote and go through the change address process to set it to 2 it will not turn the #2 receiver off. Any advice?