Bad UTF character in DOCTYPE breaks page in IE

Question

We have a search results page that worked fine but now, when viewed in IE9 it's forced into compatibility mode and breaks the layout (we don't support IE <9).

Some poking around seems to point to the opening < of the doctype being converted to an invalid unicode character, which is causing the IE grief. Why is this and what to do about it? I am at my wit's end here.

The rest of the site is fine, and this problem is only in IE. Firefox, Chrome, Safari all ok.

http://www.finecooking.com/search?cx=009096020989677304441%3Akkzh0x3f3yc&cof=FORID%3A9&ie=UTF-8&q=chicken

(you can also just search for anything)

Answer 1

It turned out one of the team members saved one of the includes for this page as UTF-8 WITH BOM, the BOM is that rogue character that broke the page. Resaving the file with no BOM fixed everything.

I can't tell you how many includes we had to check.