Remote Entry Problem

Hi,

I own a 2001 Prizm LSi and recently bought a replacement keyless entry fob. After programming it, it worked fine for several days and then *kind of* stopped working. The lock button would lock all doors but the open button was doing nothing. Despite requesting a replacement and programming the new remote, I still have the same problem.

Does anyone have any suggestions as to how I can fix this?

Many thanks :)