Hard to say. I could take an absolute wild stab-in-the-dark at it. Could you post the drawing?
Could be that something that was used to create the surface is missing now. Or it could be several other things.
Maybe start by detailing what type of surface it is, how it was built, what exactly the problem is, and where it generally occurrs.
Past that, I'd be just guessing, which probably wouldn't help much.
-Owen Windows 7 x 64 bit NVidia Quadro K3000M Dual Monitor 32.0 GB RAM Intel Core i7-3820QM @ 2.70 GHz Civil 3D 2013 SP 2 ______________________________________________________________ Usually, I find that the problem is between the keyboard and the chair.