Naked Edges-how to repair so they can be joined

This is a model built in the Mcneel training, unfortunately after lofting the curves of the mouse, there remains a faulty surface that can’t be joined. Any advice would be appreciated.
Thank you!Trackball.3dm (3.6 MB)

Your edges do not match so you can’t join the surfaces. I have just done the loft again and it joins well. Maybe you used the wrong curves/edges or you moved a surface and now you are not able to join the surfaces. If you do the loft properly you should not have problems to join.

Thank you!