Export problem - FBX file format

[pimeto]

Hello to everyone!
I have a big problem with my scene here.
Let me explain what i have, did, do and what happens.

I modeled a low poly level for a game, textured all the obj's then merged them all into one object.
The merged Obj has only one UV set (as you can see in the image below).
http://img94.imageshack.us/i/uvsd.jpg/
Then i make another unique UV set to bake lightmap - i do this without any problems. The lightmap is ok, the renders are okey... no problem at all at this level.
Then i try to export the OBJ in FBX format (because, as far as i know this format supports two UV channels).
During the export an error occurs (as you can see in the image below). The problem UV set is the main one, with all the obj's unwrapped (the unique UVs export OK).
http://img97.imageshack.us/i/fbxprob.jpg/
I really don't know what the problem is. It is very urgent, i am on a timeline here and any help or advice or idea will be much appreciated !

Thank you all for your time!


p.s. i am using XSi 2010!