The signature on the certificate was found to be invalid-Rename a person

I try to rename a person through administrator client. I am getting an error messageAdmin Process: Received the following error performing a Initiate Rename in Domino Directory request on Andrews Thomas/CA/Logica (File name: names.nsf): The signature on the certificate was found to be invalid. Check the log file for details.

Could you suggest some idea to resolve this? Thanks in advance