failure in exporting manually skinned meshes with blender

[Albi]

Hello, I have a problem exporting DirectX files with Blender:
with the last exporter I have tried to load in mine programs some DirectX armature animations made with blender and using a single armature with automatic mesh skinning I have obtained good results
but when I have tried to do the same with manually skinned meshes for finely adjusting of the mesh deformation I have got console errors like this:
File "<string>", line 1476, in my_callback
File "<string>", line 572, in writeRootBone
File "<string>", line 504, in exportMesh
File "<string>", line 693, in writeSkinWeights

somebody knows what may be the cause for this?
Thanks for any help or suggestion

[Albi]

I had forgotten to say that my blender scene does not contain SubSurf meshes, so this is not the cause of the console errors