Dear Barabba your problem is that you need to separate the road sides from the tarmac road. The road would be a racesurface (with deform=true tag) and the sidepanel a normal terrain element. The same thing happened to me when the track was exported with multiple material cross section roads. To split an object into two objects what I do is the following (3dsimed):
1. Isolate the road gmt with 3dsimed.
2. Hide road material
3. In the edit menu. Select-All faces-delete.
4. Export the object as racesurface_XX.gmt
5. Isolate the same object again (from the main scene).
6. Hide the remaining material(s). In case of different materials in both sides, they can be exported into the same gmt.
7. In the edit menu. Select-All faces-delete.
8. Export the object as XX.gmt (no racesurface this time)
9. Repeat this with all the road elements having this multiple material problem. Two parallel road lanes in a cross section (pitlane for example) may be kept in the same gmt.
10. Go to the main scene. Delete all road elements.
11. Export the scene into the same folder you exported the road and side elements.
12. Open the new_output.scn (the textures are already there if using the main folder. If not export textures from into the "testing" folder)
13. Add road and side objects one by one (from the primitives menu)
14. Review driveable and collide tags for all elements since they appear resetted to false (typical error is to forget this. See pocoyo park thread)
15. Export the scene.
16. Edit the final scn to include the new elements as you have done up to now. Deform tag in racesurface...
I hope it helps you and others as well. This procedure is a pain in the butt when there are lots of road elemnts with the problem. When converting circuits is not so bad since you just need to do it once. However, when working on a new track (especially BTB users that cannot control in how many gmts a cross section is exported. I don't know 3dmax) be careful when exporting the circuit from your design tool not to overwrite the previous gmts when no changes have been intruduced to the road. I always save those files into a separate backup folder, the same as for the textures when modifying originals after exporting.