You could have put this in the other post That should cover it, although if there's a bug in his local player profile, he may need to delete that. Pass this to him:
Go into the game launcher (7dlauncher.exe) and go into the Cleaning Tools section.
Open Game Settings
Delete that entire registry folder for the game:
Make sure there is no Mods folder in the appdata section (copy paste into the run box: %appdata%/7daystodie ). If you REAAAAALY want to be sure nothing is bad in Appdata, just either delete the folder, rename it or put it somewhere else. There could be corruption in his downloaded world, so have him delete the SavesLocal too
Verify the file integrity 3 times in a row (just to be sure, steam doesn't catch bad files every time)