Original vs "Private copy"

[Gargos]

I own the original copy of the game on Steam and the private copy. Both with the last patch, same options, same all...Well my private copy works fine and the original is stuttering like hell. I read and try lots of thinks...but the ORIGINAL copy is UNPLAYABLE. What can I do then?

EDIT: My private copy runs fine, but it's the version "1.2.633.0" the original steam version stuttering is the version "1.3.643.1". That could explain the difference between them...let's see if I'm able to set the previous version on steam.