Yahoo hosting doesn't allow files on their servers which begin with a period.
This opts out a '.htaccess' file.
According to yahoo's tech support they offer a tool in their messy user tools section called "mod_rewrite" which I can't find.
Searching for a solution I noticed that the codex is hosted by yahoo web hosting...
How do you get mod rewrites working on Yahoo?
How do you retrieve your mod rewrite rules generated by WP 2.x to put them into a tool which somehow works around using an htaccess file?