Solved the weird opening problem.
When i tried to troubleshoot the texture problem i set the model path myself, using quotation marks. Now i checked the registry entries and ModelDirectory had the data "path\to\model\"\ meaning it had one backslash too many. I removed the data and now atleast that works...
Putting the textures in the same folder worked.
Edit: Moar probs!
I have some transparent pixels on the textures. These are black, and should not be that. Does STBC support this? If so, how can i enable transparency?