I really don’t know. I have several ’tags’ on my site where I sort using the &tagData.
only thing I can think of is case sensitive, ie if the tag is xHTML and not XHTML.
if that’s not the case, my only idea is to try and setup blog tagging like in the wiki, if you get it to work following the instructions there you can adopt it to your particular case and if not you can seek help on the tagging first.
sorry mate and good luck, hopefully someone who knows better will come around