If you encounter Unable to connect to the VPN server. in MillenVPN, it is likely that your environment is not configured to allow VPN connections. (If you see the error code 809 or 87)
Please check to see if Windows Defender, a firewall between the client and server, security software, NAT, or router is not configured to allow VPN connections.

Also, if you receive a "VPN Connection Failed value cannot be set to Null. If the "Parameter name: device" error occurs, please try changing the VPN protocol setting to "WireGuard" or "OpenVPN" as described below in "If the above steps do not resolve the problem".

(1) Addition to exceptions

  1. Open the "Windows Defender" item from the device's Control Panel and click on "Allow apps or features through the Windows Defender Firewall".
  2. As shown in the image below, (1) click "Change Settings" or (2) click "Allow Other Apps", (3) browse to "MillenVPN Apps", and (4) click "Add".
  3. MillenVPN" will be added to the list as shown in the image below. Check the box (5) and click "OK" (6).
  4. Return to screen 1 and click on "Enable or Disable Windows Defender Firewall." The following screen will appear, check "Disable Windows Defender Firewall" and click "OK.


  1. Log in to MillenVPN and select Settings (gear symbol) from the left side menu.
  3. Check your environment
    If the VPN protocol is set to "IKEv2" (default setting), please check if access to UDP ports 500 and 4500 is allowed by your firewall, security software or router settings. If not, please change the settings.

If the above steps do not solve the problem, or if it is difficult to change the settings in ②, or if the following error message is displayed:
③ Please change the VPN protocol to "WireGuard" or "OpenVPN" and try connecting again.

  • The above procedure does not solve the problem / It is difficult to change the setting
  • Unable to change router settings OR unable to check availability of IKEv2 connection by another device.
  • When connecting, "VPN Connection Failed The value cannot be null. Parameter name:device" error message is displayed.

(3) How to change protocols

Please change the VPN protocol to "WireGuard" or "OpenVPN" from the "VPN Protocol" item in the "Connection" tab of the MillenVPN application and try connecting again.

    If there is no improvement even after changing the VPN protocol, please refer to the following page to check if the connection is possible with "MillenVPN Native".

    How to use MillenVPN Native on Windows 11]
    [How to use MillenVPN Native on Windows 10]