Your gonna want to rebuild the curves, so they have the same # of spans, like d24e stated. Make sure you have only 4 curves. Select the 2 side(profile) curves, then select the other two curves, the top and bottom ones (rail curves) and then Birail 2. You need to have only 4 curves, and they must all be touching. The two rails must be touching the two profile curves. Hope this helps. If your still having problems, I can be contacted at RsEagle27 on AIM.