remote c/locking dies when car warms up

[mickey]

Hi folks
I hope someone can help I've had loads of probs with my remote central locking but I thought I had it all sussed new two button plip with new box from under the passengers seat installed them no probs worked a treat but now when I run the car say for 45 mins to work it doesn't work if I then wait for it to cool down low and behold it works again and it carries on working until the car gets hot again any ideas [:D][8)]