unusual carbohydrate structure?

[DOCTORHIM at aol.com]

You probably have a bisecting GlcNAc which cannot be removed by jack bean
hexosaminidase.   This will also block mannosidase digestion.  Only
 Streptococcus pneumonia beta-N-acetylglucosaminidase will remove bisecting
GlcNAc. ( See http://www.prozyme.com/glycoenzymes/)