Is the IP address change in relation to the primary node or subsriber in the cluster?

You may or may not be aware of the following, if the IP address of the first Cisco Unified CallManager node gets changed while a subsequent node is offline, you may not be able to log in to Cisco Unified CallManager Administration on the subsequent node.

This means that when you change the primary node IP address, it is synchronised across the other CUCMs in the cluster. If one of the servers is down at time then the Primary IP will not get updated, and consequently you will be unable to login into the Administration from that subscriber.

If this is the case, then to resolve the problem you log in directly to operating system administration on the subsequent node by using the following IP address:

http://server-name/iptplatform

where server-name specifies the host name or IP address of the subsequent node.

Enter your Administrator user name and password and click Submit.

Navigate to Settings>IP>Publisher.

Enter the new IP address for the publisher and click Save.

Restart the subsequent node.

This information was taken from the following document:-

http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a008079bc04.html

Inicdentally, I assume you have verified IP connectivity? Have you changed only the host address portion, or the actual network-prefix?

Hope this helps.

Regards

Allan.