Just to clarify,editing was done within the game, not externally (i.e. using notepad).
Also, none of the reinstalls i've done have asked me for my serial number again.
TBob, did was your error as a result of editing profile?
My System
Vista Home Premium 64
Intel Q6600 Quad Core
4Gb OCZ PC2-8500 1066mhz Reaper
SBlaster Audigy 2 ZS