Make sure that you do this on a copy of the file. Netfabb can screw up a model. It may or may not fix the one problem while introducing others in the process. Sometimes, you get out OK.
I fix these in a 3D polygon modeler. KS shows me where the edge is and I go into the model and usually find a "triangle" having four or more points; where there should only be three. Welding the extras to one of the three on a corner along a common edge, and then deleting the resultant 2-point polys if any are left after the extraneous points are gone, clears the problem. Do you have a modeling application?
EDIT: Ah, good. While I was replying, you fixed it.