Symptoms
Two nodes have the same network address and one of them cannot be added to the enterprise.
Resolution
When you add a node to the enterprise, it will check all other nodes to ensure that none have the same IP address. If nodes are in the enterprise scanned in by hostname rather than IP address, then the hostnames of the other nodes will be resolved to make the comparison. If another node already exists with the same IP address, you will be prevented from adding the new node.
This check is normally a good thing, but it can be overridden by setting the following preference to "Y"
DONOT_CHECK_DUP_HOST
By default this preference will not exist, so you will have to use pref add to add it. Once it exists, you can modify it or delete it as needed.
To add this preference the syncui commands would be:
c s MASTERSERVERNAME ssdatmgr
db login sysadmin SYSADMINPASSWORD
pref add DONOT_CHECK_DUP_HOST Y
quit