Is your object scaled ? You need to call SC_AllowObjectScaling() if it is after you setup the object, if your object's postion changes at all, you need to call SC_UpdateObject()..
Perhaps try setting the object up as a complex object and see if you get the same problem...
Also, how are you detecting the collisions, what system of sparky's are you using, raycasting, sliding etc..
Lastly, I also had that same problem with sparky's with my character falling through the terrain.... it turned out the problem was where I was creating the character, it was too close to the ground, and started moving through it, before it was setup properly....
I fixed my problem by making my character model spawn a ceratin distance above the ground and to "fall" down to it.
EDIT : The exact cause of my problem was the "collision sphere", I was using sliding collision and raycasting, a mixed system from the sliding demo that comes with sparky's. Anyway, it turned out that when I created my character close to the ground, it's collision sphere was going through the ground at the point where it was detecting collision, so it didnt think it was on anything and fell... like I said above, just spawning the character in a little higher fixed it, although if you dont want your player to see your character falling to the ground you may need to hide it or exclude it or something
If it ain't broke.... DONT FIX IT !!!