Hello,
I don't have the same Net Extender environment as you. But, I can provide with some general RD connection troubleshooting steps:
First, make sure you're using the latest version of Net Extender. And make sure the RDP services are running on your new PC.
Besides, ensure that the Net Extender's VPN connection is established correctly and that there are no firewall rules or network configuration blocking RDP traffic.
The credentials stored by Windows have expired or have not been updated. Trying to clear the relevant entries in the Credential Manager (Control Panel > User Accounts > Credential Manager) may help.
Since the laptop you mentioned can be connected successfully, comparing the network settings, security software configuration, and RDP client settings of the two devices may help locate the problem.
If the problem persists, it is recommended to contact the Net Extender support team, who can provide more specific guidance.
Best regards