How can I get a .nxs convex file

Version: NxOgre 1.7, Ogre 1.7.2,PhysX 2.8.4

I try to convert a mesh made by 3dmax(use OgreMax),and try to convert it to a convex file.
.mesh->.xml->.nxs but the nxs is empty 0kb.
i try both flour 4.7,4.8, both ogrexmltoflower.rb and ogrexmltoflower.exe
i also use blender both 2.49 and 2.59 with their flower exporter.
but the nxs still empty.
when i use the runtime code,i still get a empty nxs;

the mesh has one submesh and just about 150 vertex and face.

who can help me and tell me how to get a nxs file, thx;

Runtime code:

NxOgre::MeshData* mesh_data=Critter::MeshFunctions::read(m_SceneMgr->createEntity("plane-entity-nxs","Thunder-low.mesh")->getMesh());
mesh_data->mType=NxOgre::Enums::MeshType_Convex;
Ogre::LogManager::getSingleton().logMessage("cook");
mesh_data->cook("file://Thunder.nxs");