It looks like updates to flash (CS5.5) in the last month or so have changed some things - I had a few of my ScaleForm HUD's break. I think I've figured out the changes now though. I was able to use the fontlib that came with UDK before in my AS3/SF4 HUD's. I can't anymore, getting the following error:
If you get this error, you'll need to create your own AS3 fontlib now, which luckily isn't very difficult. Basically create a new AS3 file, add the fonts (Bitstream Vera with the '$BoldFont' and '$NormalFont' names), then hit 'Export for ActionScript', and 'Export for runtime sharing'. Put the SWF filename in the 'URL' box for runtime sharing (eg: 'gfxfontlibas3.swf'), and away you go.
Error: ActionScript version mismatched between main and import '../UDKFonts/gfxfontlib.swf' files
Error: Failed to create a movie from 'C:/UDK/UDK-2012-05/UDKGame/Flash/PATH/file.swf'
Hopefully in future UDK ships with an AS3 version of the Fontlib in the 'UDKFonts' package (although I dunno if you want a double-up on fonts in this package, as it's a startup package etc... ah well, might be worth thinking about).