Object reference not set to an instance of an object

Hello good folk of Assetto Corsa mods. I am a GTR2 modder seeking to import some of his work into this wonderful sim. I dont have really much time at my disposal nor the proper tools (software wise I only have that which was sufficient for GTR2 modding - ZModeler3 and 3dsimed). So i tried importing my Porsche 910 while using the 906 from the AC Legends mod as a structural basis and replaced its mesh with mine in 3dsimed. The car loads in Custom Showroom and looks splendid:

However, when trying to open it in the standard showroom (which to my understanding is similar to how the game renders the cars in game as well) the car wont load and the following message appears: Object reference not set to an instance of an object

What shall I do with this peculiar information? I tried almost everything in 3dsimed, to no avail.

I have loads of other cars I made for a massive 1967 WSC mod for GTR2 and I would love to see my models shine in AC, without putting too much work into learning the details of AC modding that his, haha preferably....

Thanks in advance.

 

AC engine needs to have proper mesh and null objects structure to work in game, just replacing mesh is not enough if you don't put it under proper node (null object/dummie). Physics engine is looking for those nodes, not for mesh. Go to SDK directory in AC installation and there is pretty useful modding pipeline PDF file, everything is explained there. If you have correct dummies and the game is still crashing, first place I would look into is the Documents/Assetto Corsa/Logs/log.txt file. All problems why the car is not loading will be listed there.