2002 WRX MTX - This one thows a CEL in a 2004 car. (Code - P0340)
More Info about it here. Secondly, this ECU refuses to flash (in an 04 car) any image but the stock image. Odd?
http://forums.nasioc.com/forums/showthread.php?t=803560
Don't know if any of this info will help (but it can't hurt either).