I get this error a lot when trying to import models.
I have FBX set to export smoothing groups. I am using Maya 2011 with latest FBX plugin, and all my normals are set at 30 degrees. Maya doesn't have smoothing groups so they must be generated on the FBX export. If I uncheck 'combine mesh' the error pops up but still imports the separate meshes and materials. If I check it, it completely fails and sometimes crashes UDK for a bit.
Any ideas anyone?