I am not an expert on Yahoo, but from what I have read on the search engine forums, Yahoo can be picky about javascript and things like that. I would highly recommend reading:
http://www.webmasterworld.com/forum35/index.htm
They are the best source for information on many search engines - I assume they are pretty good on Yahoo too.
------------------
TopBucks.com - Converting at better than 1:130
David Lace Content - Highest Quality Teen Content
ConversionCash.com - Make Money off your WebTV Traffic