When attempting to register the vSphere Replication appliance to the PSC, you may encounter this error:
On the appliance, look in the log file /opt/vmware/hms/logs/hms.log: if you see messages similar to the following, the time of the replication appliance and the PSC may not be in sync.
To resolve, make sure the appliance and the PSC have the same date and time. The quickest way to do this, is by setting the time manually, but it is preferrable to configure NTP servers on both appliances.
Note that if the replication appliance has just been deployed, the most likely cause for the clock skew is a wrong time setting on the ESX host running the appliance. In this case, you should correct the time on the ESX host as well (either manually or through NTP servers).