Some of the first ones I did, I had to redo a couple of times. Its part of the learning process.
Save your scene so you have what you have now as a back up. and check for error on a copy of it.
What program or programs are you working in?
You may not have to redo from scratch. You can email the xfile and I will see if it open in the direct x viewer. It is a good indication if it is going to work or not. Not 100% sometimes depending on how it was exported.
It might be a scaling issue. its hard to say without seeing what you are seeing. If the pick up object will set into the map editor, but crashes when you pick it up. then I still would say check the pathing of the stuff. You can send the gunspec and the weapon fpe file and I can check them real quick.