I have a site collection with multiple sites. When I upgrade the site collection the sites all get 404. If i use Designer I can see the default.aspx file fine. If I rename it to default1.aspx then back to default.aspx the site is viewable from the browser.
I can always manually do this for all the subsites, but I would like to understand why this happens and what I can do to the 2007 site to prevent this.