I am not familiar with how Cinema 4d exporter works, however it could posssibly be your player movement code. Make sure it allows you to walk and the collision is right for both models, blocks and entities. I have had a simliar problem a while back so I thought that might help. Looking at your cave model I dont see a problem with it. GS out.
The Bounding Box is aligned to the center of the model, but it´s much smaller than the model. You collide with the bounging box if you try to go through the model. If you don´t want to use blox as Wicht suggested you could set the polygon flag for polycollision.
