Open directory replication

From Mac OS X Server FAQ

There are several potential problems you may encounter while trying to establish an Open Directory replica.

A common problem is accidentally (or otherwise) having two copies of Mac OS X Server running with the same serial number. If you try to set up one of these machines as a replica of the other, the setup will fail. You will likely not receive an error which makes clear the cause of the problem, so if you are having trouble setting up Open Directory replication, ensure each copy of Mac OS X Server involved is using its correct, unique, serial number.

You can check (and edit) the serial number in the Server Admin application, by clicking the name of the server in the list to the left, then clicking the Settings button.

If anyone knows of other common OD replication issues and their solutions, please add to this page!