Core Issue
The Cisco Unity Express Installation Wizard is unable to authenticate with the proper credentials to the Cisco CallManager Express on the same router. This happens because the https command is enabled on the router.
Resolution
The ip http server command must be enabled on Cisco CallManager Express. However, if only https (ip http secure-server) is enabled, this command does not work. Both commands must be enabled.
Refer to the Cisco Unity Express 2.3 GUI Administrator Guide for further details.