Howdy,
actually the themes are missing a killcart.html (or similarly named) page fer agoracart. I've added the pages into custom themes, but the newer x themes area bit more dynamic and adding in the page gets overwritten during updates many times. So the cpanel folks will need to update themes that have omitted this. If yer on a custom theme, you can create an .html page with the following (this is what is in ones I've made):
<cpanel setvar="headerimg=../images/topshoppingcart.gif">
<cpanel setvar="dprefix=../">
<cpanel include="../stdheader.html">
<h1>Agora Cart has been removed</h1>
<font color=#FF0000">
</font>
The <cpanel print="$FORM{'cart'}"> Cart has been deleted.
<pre>
<cpanel Cgi="killacart($FORM{'cart'})">
</pre>
<br>
<br><br>
<center>
<font face = "helvetica" size = "2" color = "#ffffff"><b>[</b> <a href = "index.html">Go
Back</a> <b>]</b></font>
</center>
<cpanel include="../stdfooter.html">
then name it: killcart.html
then upload & copy over to the acart directory of yer theme.
Hope that helps,
Mister Ed