Iis – getting the error “%1 is not a valid Win32 application.” when I try to hit any non-html page

I'm trying to setup a development environment on a Windows XP x64 machine, so I'm using IIS 6.0 and I've gone through the steps outlined here http://support.microsoft.com/kb/894435 and currently when I start IIS it shows the ASP ISAPI filter, but when I try to hit an aspx page it doesn't work. I've double checked that the filter is from \Framework64 and not \Framework. Any ideas on how to go about debugging this? I'm out of ideas on what might be wrong. I can provide more information if necessary.

UPDATE: Ended up being that I hooked Coldfusion to IIS when it was in 32 bit mode, then switched the 64 bit mode for IIS connectors which obviously CF hadn't set itself up for. Unhooking CF and then reconnecting fixed the problem.