"The authentication certificate received from the remote computer has expired or is not valid"
Please follow the below steps on server,
Go to run -> gpedit.msc
Local Computer Policy.
- Computer Configuration
- Administrative Templates .
- Windows Components.
- Remote Desktop Services (OR Terminal service).
- Remote Desktop Session Host (OR Terminal service session host).
- Require use of specific security layer for remote (RDP) connections - Double click.
- Enable Then select Layer RDP and then Apply & OK.