ActiveHTML: AJAX does not work as expected

Please make sure that Request-Header "HTTP_X_REQUESTED_WITH" is set in Ajax-Requests.

You may do this by adding the following code to your Ajax-Scripts:
xmlHttp.setRequestHeader("X-Requested-With", "XMLHttpRequest");
Many Ajax-Libraries (like Prototype, jQuery, Mootools and YUI) will set this header properly.

You may also try to turn off ActiveHTML config value HcSendEmptyCharset, but this may have unwanted side effects.