Cars and tracks problem

[Empire City Cop]

Hi guys. When I try to play a custom track with a custom car it does not work. Instead i get a loading screen, a crash and a exception caught. I am using a police tahoe traffic car on it and oh by the way the track is lake diabolo. Any ideas. This happens on any track except the ones with 'Sedan' as the police car. P.S HELP!!! P.P.S
On caprice,suv and sedan folders I am using custom police cars that are all in the polycount.

[Roadstar]

Maybe its serial no. conflict. You will need Serial No. Edit or NFS Wizard for that & open fedata.eng file in it.

[Freak-DS]

Your player cars might b too highpoly.