I've seen that problem. I believe one time it was when I tried to use an Offset Alignment, and the Offset Alignment was going in the opposite direction from my Baseline Alignment. Then I seem to remember another time where I couldn't ever figure out what Civil 3D was complaining about, and I drew the boundary in manually.
-- Sinc
http://www.ejsurveying.com
http://www.quuxsoft.com
Sinc