I also have exprienced a problem with FBX.
It was some 2.5 version also
I had to re install Blender 2.49 to be able to export to FBX 3DGS without problems.
That's strange but i don't find the new version of BLender really simplified !
Why they don't have put icons for each things like in Maya ?
I find the interface have too much menus !
Why they don't make interface things like in Silo or other great tools ?
Simplified and clear ?
I find more clear to work with the 2.49 version, perhaps beacause
i use it for log time ago ?