Hello James,

to open the script editor got to Window > General Editors > Script Editor or press Shift + s.

Without seeing what it says there could be a couple of reasons that your mesh didn't convert.

1: The maximum base mesh faces (in the convert poly to sub-d attributes) are set too low, it should say, in the script editor, when you get the error message what amount you need to set it to.

2: There may be some non-manifold geometry on the model, use the Cleanup option under the Mesh menu (maya 8 and above) to sort this out.

Hope that helps,

Mat.