You have some kind of non-manifold geometry (geometry that cannot be unfolded). There are three kinds of non-manifold geo - three or more faces sharing a single edge, two or more faces connected by a single vertex, two faces sharing a single edge, each with opposite facing normals.
To clean them use mesh>cleanup with the non-manifold geometry box checked as Dave suggested.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675
Last edited by ctbram; 14-09-2011 at 03:50 AM.