I notice it's still not working, and the CSS3PIe site still claims that it enables support in IE 6-8...

Has the cause been found / is a fix planned?

No, I still haven't been able to reproduce this issue. Plenty of other people are also using IE6 with success. So without knowing how to reproduce it, there's really nothing I can do.

If anyone who is can reproduce the issue is able to do some investigation, it would be greatly appreciated.

Unfortunately as it's a work PC which is locked down I can't install any debugging tools so don't think there's much I can do to diagnose the cause myself. Perhaps someone else experiencing the same issue might have more opportunity to do so?

You saying it's "locked down" got me thinking... is your browser using the default security settings or a customization? Could you check the value of Tools->Internet Options->Security Tab->Custom Level...->Binary and script behaviors? If it's disabled that would certainly explain it.

It's so locked down that the "Security" tab doesn't even appear for me, so I can't see what is set...

But the IE PNG Alpha Fix by TwinHelix works fine and that uses HTC so CSS3PIE should be able to load the same way...

Do you have a unit tests page or some other diagnostic script (perhaps with some sort of debugging info outputted to the page) that I could run?

I just realized this morning that css3pie.com was not sending the correct content type of text/x-component for the .htc file, despite my having included this in the known issues documentation. Whoops!

This could very well be the reason why your IE6 isn't executing the behavior. Could you please check the site now that I've fixed the content type and see if it has started working?

That sounds promising, but surely that's not absolutely necessary for HTC files to work?

Anyway, I will certainly have another go once I'm back at work tomorrow...

Hurray, it works!

I see it's already a "known issue" on http://css3pie.com/documentation/known-issues/ but I suggest this should also be clearly mentioned elsewhere, as almost nobody will have the correct content-type already set up on their server, and people are unlikely to test in IE6 either so may never discover it's not working.

Yep, I agree fully, especially since I myself got tripped up by it!

It's not working again, think you've broken/reverted something...