When I ran my website through facebook lint (http://developers.facebook.com/tools/debug) …everything was fine.
This was my doctype before:
<!DOCTYPE html>
Then, I added the “xmlns” to my doctype.
<!DOCTYPE html xmlns="http://www.w3.org/1999/xhtml" xmlns:fb="http://www.facebook.com/2008/fbml">
I ran it through Facebook Lint again…and facebook could not scan any of my meta tags anymore. Why? It said all the properties are missing.
The xmlns properties go onto the <html> tag, not the doctype.