FBX file is in an unsupported older format.
This error results from the FBX mesh importer when attempting to submit an asset which contains an FBX file in a file format older than supported by the importer. The FBX importer currently supports FBX mesh files with versions between 7100 and 7500 inclusive. Newer format versions may import correctly. Older format versions will fail with this error message.
If you are exporting from Blender, please note that Blender's FBX text exporter appears to be older than its FBX binary exporter. If you are receiving this message while using Blender's FBX text exporter, try swapping to the binary export mode instead.