Hiya

SubD's are somehow like a diva. The do refuse to work when the geometry is not the way it should be.

Check the script editor. I bet there is something like "nonmanifold geometry" written in it. Try a Cleanup with the "clear nonmanifold geometry" flag set.

Anyway Maya tells you excatly where the problem is, even if it can't fix it. If you don't find the face or vertex which is causing the trouble, copy the little fellows name from the script editor and paste it in the quick select box on the upper right.

For time saving reasons, it sometimes makes more sense to delete the trouble face and put in a new one instead of trying to fix it.

good luck

---mac---