well did you open the script editor and look for details?! If you had i'm thinking that it will probably say something about the fact that you have too many or too few original faces or some crap like that. Up the number in the options box and you should be fine after that. Either that or it's bitching about non manifold geometry. In which case run poly cleanup on it and make it get rid of the non manifold stuff. Or find it yourself (look for oddly shaded (black) faces) and make sure that the polys are planar.

Alan