I've run across similar issues in the past.

My troubleshooting usually begins with "have I installed anything new"?

The last time I was having a X-10 issues it turned out it was my new laptop that was causing the problems. I had it plugged into a non filtered outlet. I unplugged it and and the X-10 was back to normal. A new filter solved that issue.

Now those dimmable CFL's are my next problem. The buzzing is driving me nuts.