“The page you are requesting cannot be served because of the extension configuration.” error message

I’m getting this error message when trying to run my application. I don’t know how to fix it:

HTTP Error 404.3 – Not Found The page
you are requesting cannot be served
because of the extension
configuration. If the page is a
script, add a handler. If the file
should be downloaded, add a MIME map.

Here’s a screenshot of the error page:

What can I do to fix this error?