OBJ gravity sketch to CREO solid

Hi everyboby,

I use gravity sketch on my oculus to create form, and export an OBJ file with the mesh.

After, i want to convert this obj file to a solid in creo 5.

I open the obj file, and export it to a shrinkwrap. and when it calculate, no surfaces is create.

I don't know why sometime it work, and sometime doesn't.