After hours of failing to find why I was getting the following in IE:
Message: HTML Parsing Error: Unable to modify the parent container element before the child element is closed (KB927917)
I finally identified the culprit. We had a user generated tab 'Multimedia' that we had placed YouTube video's in. After removing the YouTube embed code this now works properly in IE. It totally and completely sucks because we built the site in FireFox and QC'd IE6-8, but we never checked the products that had videos (which is a lot of them). FireFox (and pretty much all other browsers) handle TPP and YouTube embeds without issue.
This is not a minor issue where an exception is quietly thrown, IE6/7 will fatal error and throw up a 404, IE8 will load the header only, in compatibility mode it loads the entire page and will throw a quiet 'Done with errors on the page'.
TPP is great, I have to find a way to deal with getting videos to the users that does not include a tab.
I was somewhat disappointed that placing the embed outside <!--@EndTabs@--> did not help.