ok, this usually fixes all nurbs problems... If you are sure that your surfaces should stitch but dont, its probably a surface anomaly. I dont know why they happen but the happen. this process will work for most annomalies

Export the surfaces to IGES files. Together or seperate makes no difference. start a new maya scene and import the IGES file(s). Perform stitch.

Hope this helps.. my trick bag is now empty.