After upgrading from 12.8.1 to 12.8.3, I got a Tomcat error 400, "Request header is too large" after installation. I needed to edit bin\Tomcat\conf\server.xml and add maxHttpHeaderSize="65536" to all four <Connector> tags.(two for port 8081 and two for port 8443) After restarting the WebHelpDesk service, it came up fine.