Maybe this part of the 'Read me' explains the problem?
"IMPORTANT : DEDICATED SERVERS:
If you are running this mod for league races and have a dedicated server (i.e. use server.exe instead of NR2003.exe) then please install the "Dedicated Server install" version of the mod instead of the full one. In testing we have found the full mod will randomly crash a server, and sometimes won't load tracks at all, we believe this to be related to the way the server.exe handles mods which is different to the regular game exe, we are still trying to narrow down the issue so created the dedicated server install for launch - but the other advantage is it's only 2MB total so saves a ton of space on the server, see readme for specific installation details. This does not need to be used if you are hosting a race over IP via the Multiplayer "Host" option from within the regular game (NR2003.exe). "