Some Solutions that I have found:
Problem 1- The structure of the weapon shown while selecting character then crashs when login
Solution 1- There are something wrong in your 2D ( .ddj )
Problem 2- client crashs after clicking connect
solutoin 2- Actually there might be more than 1 solution
- wrong export settings you should select all of those
Export settings
-Selection Only
- Include normals
- Include Uvs
- Triangulate face
Import settings
deselect everything except Keep vertical order ( Poly group )
- Second solution the size of the weapon or whatever you edit might be big ( Iam not talking about Mega bytes ) Iam talking about Size of the structure it self
- Third solution might be missing bones ( which I didn't face till now )
- Problem 3-
You are logging in but you can't see the weapon
Solution:
- You must use the ( US support version ) of the converter
- You should use blender ver 2.63
- You might moved the weapon during you edit to another space so it didn't display at the correct place
Others I don't know
Hope those tips help someone

Thanks
btw sorry for my bad English, and there might be something wrong else other than those.