The FBXConverter tool is old and, most likely, you are trying to convert an FBX file with a recent version that is not supported by this tool. You can try to call directly the command line tool found in the bin folder 9C:\Program Files\Autodesk\FBX\FBX Converter\2014.1\bin).
you can just type FBXConverter /? for a description of all the options. But you will quickly see that this executable is limited in the supported FBX versions.
To be able to convert a more recent FBX file, you will have to build your own "tool". This is actually easier than it sound, provided you have a minimum skill in building C++ programs. The FBX SDK package comes with a number of sample code that you can look at to be inspired. The only thing you really have to code to convert an ascii FBX to a binary one, is to read the file and right after save it in binary. You can just slightly modify the ConvertScene sample to skip writing to the other formats 😉
Hope this helps!
Regards
