Is it a server he runs on the same computer he plays?
I know that the server doesn't need all the files.
The surfaces are needed to insure no ''cheating'' with values like road grip for example.
And layout ini files are needed as well.
The rest like kn5 could be skipped.
But that only makes sense if the server is on a different computer/ dedicated server.
I'd say to tell your friend to get the vip already, but from what you say, I'm not sure it'd fix anything!
I could think of checking file integrity with Steam on both games just to make sure it's not other altered files that mess up with the checksum, but meh.
And also try a server with a kunos track to see if that works, that would be a good start
yes the server he runs on is the same computer he plays on.
And yes we have been drifting and such on that server for a couple years now and we can play any map without problems. We tried multiple versions of custom shader patch.
We also both have the full reset from steam and the map runs perfectly on singleplayer for both of us.
What still bothers me is that the server gives a checksum problem for him as well eventhough its legit his files from his game that work in singleplayer