First: when you embed a font in your xml, the "id" is NOT free: it has to match the (case-insensitive) name of the font displayed by your system.
I.e: the file is called Florsn33.ttf. I click on it, FontBook returns a window called "Florencesans Black" => in my xml, the id must equal to "florencesans black" at least.
The tag is looking like this:
font id="florencesans black" import="[...]/Florsn33.ttf" glyphs="abcdef..."
Placing id="florB" => the font will not be found/displayed.
Second: it's impossible to load external png! All png's as to be included in the swf with swfmill to be displayed. No problem with ids here
Maybe it's explained in the doc, but i don't like reading it...