When I migrated our Mura site to our new IIS7 servers, one problem I noticed is that the Mura 404 handler was no longer showing. Instead the default IIS 404 page was displaying.

This problem doesn’t only apply to Mura, it will crop up with framework or code that uses the onMissingTemplate handler. The fix is easy. Edit the web.config file in the webroot, look for an httpErrors tag. It might look like this:

You need to add existingResponse="PassThrough" to it. If that element is missing completely, just add it with the necessary attribute.