Hi

I've just been playing around, trying to learn how to use poly's, and here's a big problem I've run into.

Here's a screenshot


Wireframe, of the offending area


Now, when I try to delete the edge which is circled in red in the above picture, all chaos breaks out.



I have constructed this shape from two polygons, and merged the bottom verticies as shown below


Wireframe




Can someone please explain what I'm doing wrong?
This edge shouldn't be doing anything, so surely I can delete it?!