Unable to add client node in Rapid recovery core dashboard

Hello All,

I'm facing one issue I'm unable to add one client server in core dashboard.Its giving following error:-

Value cannot be null. Parameter name:Source

Can anyone please help me out.Support team is telling to upgrade the Core version form 6.2 to 6.3

Agent version is 6.2

Agent OS:-windows 2012 R2 Standard

Core version:-6.2

Core OS:-windows server 2012 Standard

Error log:-

WARN  2019-11-21T08:13:10 [20] - Replay.Agent.Management.Authentication.AgentPairingClientCertificateAuthenticator ()

Request client certificate thumbprint 'C355AEFC0649A62C83326737770F64F8DE428EFD' does not match previously paired client certificate thumbprint ''

Please suggest