Well, Richard, that's interesting. If you don't mind, you could post the SVG here or mail me (matma.rex@gmail.com), and I'll try to find the problem.
I also have one idea - you're using rectangles on your map, and if Inkscape decided to store them as <rect> elements instead of <path>, the script will fail - I'll try it out tomorrow (it's 2 am here already and I'm off).