This file is a stand-in for the magic "scriptx:" URL, that SiteMill strips off and reports as an error.

I wrote a ScriptX extension that registered ScriptX with the web browser, as the handler of the "scriptx:" protocol. What that means, is that when you clicked on a link to "scriptx:foo", a
message was sent from your web browser to ScriptX running locally on the same computer, and it can parse the URL and handle it any way. Check out the ScriptX Web Module Documentation for more details.