Power Lock

Hi,
I have a Honda Accord 2000, SE Model. My car has a peculiar problem. I am not able to control the passenger side locks (the front non driver door and the door behind it) using my remote. This problem does not happen when I use my remote for the first time in the morning. Everyday morning when I unlock the car using my remote all the 4 doors unlock properly but from the next time onwards for the rest of the day the passenger side front door and back door will not open or lock using my remote. The remote again works properly if I try after a long break of half a day or so like leaving the car at office in morning and then try unlocking when I return home in the evening. I am able to operate all the 4 doors manually though. This problem started with the back door of the passenger side and now has spread to the front door also. What could be the problem?

Regards,
Mags