I have a couple of questions before we get too far.
1. Do you have a yahoo account?
2. Do you have a site map installed on your website? But for yahoo if you have an RSS feed from your site, that might work instead of the site map generator.
Log into your yahoo account, then go to the site explorer page.
https://siteexplorer.search.yahoo.com/mysites
Submit your site, verify your site, and then submit the site map or the RSS feed.
This is kinda like yahoos version of google webmaster tools. Once you get the site explorer up and running, you will be able to get more information directly from yahoo. Then you will have some real information to work with. This would be a lot better then trying to guess what the problem is.