Source: Release Notes
HTCs / VBScript
HTML Components (HTC) and VBScript code when used inside of an IE9 or IE10 standards mode page are no longer executed in compatibility view.
Consequently, DOM APIs used by the HTC or VBScript code now behave according to the IE standards mode version of the same APIs.
However, the MS HTC documentation has several examples of basic HTC implementation that works on IE9 (eg. Microsoft MouseOver Hilite Sample)
I tried to copy over the exact same example MS used and place all the necessary files on my server (My MouseOver Hilite Sample), but it doesn't work on IE9.
I tried a simpler version, but it also didn't work (Testing IE9 HTC).
While viewing the Developer Tools window, all three examples show the same browser mode (IE9) and the same document mode (Quirks).
The only difference I can find is when I have Fiddler2 loaded to log the headers.
Microsoft HTC Example:
My Microsoft HTC Example:
My Simple HTC Example:
As you can see, the HTC file is not even being loaded on the pages on my server, but is on the MS site.
I've tried adjusting the security settings via Internet Options in IE9, but no luck. All three examples work in IE8, though...
Have I forgotten something basic like adding a semi-colon somewhere or is it more complex like I need to be facing south by southwest while chanting the Star Wars theme music as I'm about to sacrifice a goat?