Your network contains self-intersecting polylines

• Self intersection is usually a result of poor digitising.  They can be hard to spot if the intersection is very small.  Experience has shown that it is typically the misplacement of a single vertex.

• A self-intersecting polyline can be corrected by entering edit mode, setting the task to "modify feature", enabling the Edit Tool button (), right click on the incorrect vertex and delete or move it.

• In the example image below a single vertex is misplaced (red circle).  Delete vertex has been selected from the context menu.