I just made this model and exported to .obj, remaped the UVs and tried to render the .obj model....and I got this (attachment)...can you tell me why?

I am new to NURBS modeling, so please let me know the correct method of modelling it too...

I just modeled the box..filleted it...created the keys shape...extruded the keys together....used boolean difference...filleted the edges of the holes....copied the newly created keyhole faces....pasted them again...extruded them together....thats pretty much it...have i done wrong somewhere...pls tell

Thanks

Abhay Vir