Hi William. Welcome to the madhouse.  
M98toBGL works best on simple FS98 designs. There's no guarantee it will convert all aircraft. The best option if you get any kind of error message is to find another version of the aircraft by a different designer. You might like to try the later MDLtoBGL which can handle more complex FS2000 designs. http://www.avsim.com/hangar/utils/mdltobgl/id43.htm
I find this a tad buggy & prefer M98toBGL despite its limitations.