Just in case I was not clear enough:
It means that after adding the AJAX capability to the web site, the CssClass properties in all controls ( like in CssClass="Test" ) ceased to work.
For instance, in the above example, the “.Test” settings ( position:absolute; left:450px; top:110px; z-index:3; color: #0000ff; font-family: Verdana,Arial,Helvetica; font-size: 15px; ) stop working.