I get this error working with Blender while I try to assigning armature's bones to an human mesh.
The OP originally posted this in their question.
If it happened to you too and you were looking for any solution, I solved in this way:
- select mesh in edit-mode;
- in the bar "Mesh tools" select the voice "Remove Doubles" (that remove duplicate vertex).
Here there's a video that explain the procedure.
Another way to solve the problem would be add a modifier to the mesh:
- "Decimate" modifier.