I have installed the AJAX extensions and partial page rendering works ok
from a new ajax enabled web site I created in VS. The problem is that I've
manually entered the necessary entries into the web.config into an existing
project and the same asp.net file doesn't work from the migrated web.config
project.

When I compared the html source between 2 identical asp.net files the
differences was that the 2 script sections below were missing:

<script
src="/WebResource.axd?d=Htewp0TRJI3R2gJ_WhDDtA2&amp;t=632966009958750000"
type="text/javascript"></script>

<script type="text/javascript">
//<![CDATA[
Sys.WebForms.PageRequestManager._initialize('ScriptManager1',
document.getElementById('form1'));
Sys.WebForms.PageRequestManager.getInstance()._updateControls(['tUpdatePanel1'],
[], [], 90);
//]]>
</script>

Can someone explain what web.config setting controls this output into the
html?

Thanks,
Tony