Try the Lamp Module in a few different locations. Maybe even the same outlet as the CM15A. You may have power line noise, signal coupling between the two incoming power lines or signal absorbers. Killing the X10 power line signals between the CM15A and Lamp Module location. If it works in some locations and not others. You have power line coupling and signal issues.
Is the CM15A on the same power as all the computing equipment? Computing equipment is one of the known X10 power line signal killers.
The later Lamp Modules (2007 and above) have soft start where they ramp On and Off. The older ones did not. If you had an older one you have to use the Older Lamps (No Soft Start) list of modules or they would not work correctly.
If the lamp modules where from your long time ago. They maybe the older ones that do not have Soft Start and need to be chosen from the Old Lamp List.
http://kbase.x10.com/wiki/SoftStartHere is a link to some great X10 Troubleshooting Tutorials.
http://jvde.us/x10_troubleshooting.htm