it needs to be one of the values from the listing provided in
http://forums.winamp.com/showthread.php?t=303241
with the version of things you're using, you can still put more genres in the genre string _however_ the YP will after processing of the string choose what it thinks is the most appropriate from what was provided. and in that scenario, everything which was set as the string will then appears as the 'tags' aspect for the listing, but you're running the risk of having the wrong genre for the listing.
only way to control the genre and the tags aspect is to use a v2.2 DNAS based setup.