I've had some experiences like this. I don't know for sure, but I think the amount of RAM can be the problem. When I got more RAM i was able to import more complex files. Also I've noticed that .cob-file import very quickly. Much faster than .3DS and .dxf files. I seams like a more stable import too, since I've been able to import a 2 milion poly test-file in .cob format but it crashed at 30% in .dxf format.

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