OK, I believe I've found the solution.

I changed the file DesktopModules\CuteSoft_Client\CuteChat\Admin\LiveSupport.aspx so that line 3 now reads:
<%@ Page language="c#" AutoEventWireup="false" Inherits="CuteSoft.Chat.UI.ChatAdminPage" %>
Instead of:

<%@ Page language="c#" EnableEventValidation="false" AutoEventWireup="false" Inherits="CuteSoft.Chat.UI.ChatAdminPage" %>

What affect will this have on the application?