Most likely the result of a geometry error (e.g. body inconsistency, self-intersecting face, etc). If this body was imported (or you don't need to keep the feature history), you can run heal geometry and/or optimize face; these commands can sometimes fix minor errors. If these don't work (or you need to keep the feature history), run examine geometry to help narrow down the location of the error. Sometimes a minor tweak to a feature's parameters will fix it, other times it requires extensive rebuilding.
