WordPress MU

All blogs on my site are using following URL for their RSS feed: http://mysite.com/blogs/username/feed/

All, except one, which gives a "Error 404 - Not found" when using that URL. Instead, I need to use http://mysite.com/blogs/username/index.php/feed .

Why is this URL different then for the other blogs?
Is it stored somewhere in the database?
Can it be changed?

Per the readme file and the debugging script, please use the correct URLs. We can't help you unless we're seeing what is occuring.