I get that error whenever I try to import my mesh into Mudbox, and I have no idea where it is or how to fix it. Any kind of highlighting from Mudbox doesn’t help because the model rendering doesn’t work (ends up like this).
Remove doubles doesn’t do anything, so it’s not just a hard edge case. I’ve tried googling the subject, but there’s no references of Blender specifically, only Maya and the like.
Is there any way to find this problem vertex and deal with it?
Hmm… Let me perform a quick analysis of the message (note I don’t own Mudbox nor have I ever used it, so I may be completely wrong here). Vertex Valence is basically an amount of edges that are connected to it. “Interior vertex” most probably means that the vertex in question is somewhere inside a patch of faces, i.e. is not on a non-2-manifold edge, for example. This means that somewhere in your mesh you have at least two ngons: polygons with a divided edge between them. I’d advise you to search for ngons in your model and deal with them, either by hand (using Select Similar menu (Shift+G), or by employing Mesh Lint addon).