To convert FBX files to or from different versions of MotionBuilder, you can either use the Python FBX Export tool or the FBX Converter.
The FBX Converter is a free utility that lets you transfer FBX files between different versions of MotionBuilder. It also lets you convert you FBX files to OBJ, DXF, and other 3DS files to the FBX file format, and vice versa. It enables you to transfer your entertainment, design, or visualization project data from one 3D application to another – including any professional 3D animation package.
To download the latest FBX Converter: