ELMAH on IIS 7.5 causing HTTP 404 error

So, create an ASP 3.5 site using ELMAH.

It works fine in IIS 5.1, I can see all error pages, etc.

Set up the site on a different machine running IIS 7.5.

Now when I go to /admin/elmah.axd page I see 404 error from IIS 7.5.

Any thoughts on what I should be looking at?