You should only need one controller.

It sounds like you may need a phase coupler. X-10 often has issues getting from one 110V branch to the other 110V branch.

This is what I use: [Link: smarthome.com]

I've tried the coupler type that plug into an outlet and didn't have much luck with that type.

What brand of lamp modules, wall switches are you using? Insteon, X-10? Knowing the brand may help with troubleshooting your problem.