vRO with vSphere Replication - server certificate chain is not trusted and thumbprint doesn't match

Hi

New vRO 7.6 appliance with VR and SRM plig-ins installed.

I've added 'local' and 'remote' vCenters and can get back info from both.

VR plugin picks up both instances and one works ok but the other gives me a message -  Error in plug-in server certificate chain is not trusted and thumbprint doesn't match

All VR and vCenters have default self-signed certs.

Don't understand how one side works but the other doesn't

Any ideas what i can do to troubleshoot and resolve this error?

Thanks

Mark