Just another idea:
Maybe the editors you are telling are searching in the registry to find where is GP4 !
I don't know how reacts other editors when the gp4 reg key is corrupted, they surely not find the game and maybe telling you it is an unknown gp4 version.
All i could advice you is to download my TyreSet program which provide a function to specify or re-specify gp4 path to re-reg GP4 correctly in the registry.
This way you will be sure your registry is ok.
Hope you will find the matter.