I just about had a heart attack trying to figure out why my dynamically loaded Greek letters would show up just fine the first time I’d go to my site, but be garbage the next time I’d visit. I tried everything: Embedded ALL the fonts, tried saving my XML in other editors, etc. The only thing that solved this problem was adding the following code to the top of my actionscript of the SWF.
System.useCodePage = false;
You can actually see the difference in flash when you test the SWF, change the boolean between true and false.