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?