Re: HttpHandler Error - 404

I see that this thread is old but I'll still post my solution since it seems a
bit scarce:

Right click the root node in IIS (computer name of the server).
Click the mime-types button and add the MIME type there first.
Also, right-click your web site and add the MIME type there.
Add the handler in the web.config file.
Restart IIS and the WWW publishing service.

Since there is a wildcard mapping on IIS 5.1 that catches all file extensions at
the root IIS note, yet there is no such wildcard mapping in IIS 6.0, adding the
mapping at the web site level doesn't work.

 Let me know if that helps.