Big problems come with X-10 on two phased houses. Where they will split the house into two phases. X-10 has a very hardtime crossing from one phase to another, If you house has been wired like this, contact your electrician and X-10 and there is a device that can be installed in your breakerbox to bridge the X10 signal on both phases. I have x10 installed on GFCI's and havn't had a problem. But I use the x10's before the gfci not after like most people do.