Ajax Control Toolkip Collapsible Panel Not Collapsing

In the Ajax Control Tool kit there is a funky collapsible panel which is demonstrated here:
http://www.asp.net/AJAX/AjaxControlToolkit/Samples/CollapsiblePanel/CollapsiblePanel.aspx

If your panel opens but then when you click to close it, it sort of half closes then re-opens. The error is because your web page does not contain the correct doc type heading.

[DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"]

is the kind of thing that should be at the top. I am having trouble displaying the actual code here because it will affect this web page. however look for this line in the collapsible panel header.