This is just an FYI for those using X10 with the PSC05.
After many years, I decided to revisit an X10 project I made (here).
The old project used the pre-v1 of the IDE, with v2 of the "classic" x10 lib.
When refactoring for newer IDE, I used v4 of that lib.
From my observations, I found that the v4 lib was much less dependable in transmitting then the v2 version was. I went back to the v2 lib and simply changed the "WConstants.h" in the .h and .cpp to "Arduino.h".
The v4 lib was refactored to use the wire schema, and also omitted the "repeat transmit" functionality that the v2 had. I'm not sure if the loss of this is the sole cause of it being less dependable. I typically repeat the command twice though.
I know there are several other x10 libs out there, some including the receive code I wrote, and I can't say that they are more or less dependable in transmit then the v2 lib. However I wanted to share this observation. The x10 system is undependable enough without this added variable. 
If you have trouble finding the old v2 x10 lib, you can get it here for awhile.
John