there are not touching The birail is a very picky thing - also make sure the history is deleted on the curve....also a good guess would be that you have once before made a surface, but deleted and remade.. If this is the case then yes it is VERY fussy - It is almost quicker to make a new curve over the old one and then delete the old one, I have had this problem many times. But the first thing I would check is that your curves are touching, your curves match points (rebuild curve) and that the curve direction go the same way (curve direction - reverse)