Hi James --
Sorry, should have explained it better..
Let me re-cap:
1. I would ungroup the shape.
2. Verify that the end points overlay each other, exactly.
3. Identify both shapes, and then do the Shape > Operations > Join.
4. Then apply the fill. If that doesn't work, then,
5. With the shape selected, go to Window > Show Shapesheet.
6. Scroll down to the Geometry section if it's not already visible. There should only be Geometry1.
7. Upper left corner has the entry: Geometry1.NoFill. In the box (cell), to the right make sure it says "False". If it says "True", just type in a "0", no quotes. Visio will convert it to false.
Now your shape should take on the fill color/pattern.
HTH
Wapperdude