It means either
1) The resource CITcustomMaps has been modified and not restarted
or
2) The client is having problems downloading 'cars.luac'
If the problem is only occurring with one player, ask them to manually delete the client cache of cars.luac by deleting:
Go to your C:/ Program Files (x86) \ MTA San Andreas 1.5 \ mods \ deathmatch \ Resources \ CITcustomMaps
- Open the folder, delete cars.luac and then re-start MTA.