You have changed the two contrail files in your effect folder. What you need to do is put in disk one of COF then extract gameone cab to a dummy folder not to FS2004 then opne the efects folder and look through you should find two files together that control the contrails when you compare these files with the ones you now have you will find that they have different modified dates the ones in the cab file is the correct one just copy the two files over to your effects folder & overwrite. I had made a post about this not long ago & another one back in april.
MODERATOR maybe we should put this into the hot topics folder for everyone to use.
Look back to the JULY 29 posting & you will find the names of the two files involved