It sounds like you might have a phase issue. There are several good threads that cover this and all you need to do is a search for phase couplers and or coupler/repeaters. You may also want to check out how to map your electrical circuits so you have a good idea of what circuits are on what phase. I think it was put together by Puck and is an excellent tutorial.
(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)---(http://www.bdshost.com/X10/lpup.gif)----KDR