I thought I'd already blogged about this, but Google says no (or my search-fu is not strong this morning), so here it is for posterity.
If you have an old Adobe (nee Day) CQ 4 system using CRX 1.4.x and need to move the server (or just CQ instance) to another IP address, you will run into an issue where the CRX repository will not start up because it's trying to use the old cluster information (even if it's a single system, by default it sets up a cluster with one node). So it tries to connect to the previous IP address of the master cluster node, ie your old IP address. Which hopefully fails, unless you still have the old IP address active in which case it could do all kinds of wacky stuff.
To fix this, shut down CQ/CRX and rename/remove all files called listener.properties. They're located in control folders under various parts of each repository.
For example, here are the files on a CQ 4 dev system I'm updating that has both author and publish CRX instances (in CQ/AEM5+ there's just one repository):
The files should be be recreated next time the system starts up using the new IP address.
Adobe reference doc is here, see the "Cluster Interconnection" section near the bottom of the page