Previous post have error and missing?

I want to move my zimbra user accounts to a new server, here what I found to export the users, but run into some error:

[root@zimbra ~]# /opt/zimbra/bin/zmmailbox -z -m "yjvoo@example.com" getRestURL “//?fmt=tgz” > /tmp/yjvoo.tgz
ERROR: zclient.IO_ERROR (invoke sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: signature check failed, server: localhost) (cause: javax.net.ssl.SSLHandshakeException sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: signature check failed)

Any idea how to fix it?