The reason could be that there is not a problem with the remote control but with the receiver unit inside the device which ignores the signals. The solution could be to reset the unit.
So it like follow:
1) Pull the AC-Plug of the unit. (Take really the AC-plug and not the plug at the device)
2) Than when device is switched off the AC press the "ON"-button several times to discharge all internal parts.
3) Than please wait for about 2 minutes
4) Put In the AC plug again
5) Switch On the device and test the remote control