in 3ds max when ever i delete and create any faces or i extrude i always get stl errors why?

yes i have ignor back facing turned off and it still says i have errors

I hate that about stl check. it should check evrything everywhere automaticly. Heck, I just hate stl check in general. it dousn't detect lots of stuff that tool has problems with. For creating faces, make sure you connect all the verteces that surround the hole, and don't skip any. For extruding...no idea. It should have no problems extruding a regular face. I don't know why it would create problems.

STL Check = not good

Export a jms, compile it as collision-geometry, and see if there are errors.

yeah the only thing bad about that mythril is the fact that i have to spent up to 40 hours on something then i can only find out its crap in tool... oh well i geuss its the only thing you can do
btw: if you download a vehicle model with alot of open edges (up to 2000) can't you just make a rough shape of it with no open edges and use that as a collision model?

Why would you need to wait that long for 3ds Max?

As for the collision question, that's interesting
A friend of mine asked me the same thing.
As for the answer, I'm not sure, but I'm pretty certain that you have to have matching model and collision.