Troubleshooting Tip: How to fix the error 'Unable to establish VPN connection. The VPN server may be unreachable (-6005)'

[spoojary]

Description	This article describes the case when logging into the FortiClient it shows the following error 'Unable to establish VPN connection. The VPN server may be unreachable(-6005)'.
Scope	FortiClient, FortiGate.
Solution	When trying to establish a VPN connection, users receive an error message that says 'Unable to establish VPN connection. The VPN server may be unreachable (-6005)'. Check the configuration if everything is correct. It can be possible to solve the above issue by uninstalling the current version of FortiClient. To ensure a clean uninstall, use the FCRemove tool. Details can be found at: https://community.fortinet.com/t5/FortiGate/Technical-Tip-How-to-download-FortiClient-and-FCRemove-e... Reinstall the same version of FortiClient or consider upgrading to a newer version if available. When trying to log in again the error will not appear and the connection to the FortiClient will be successful. Additional Tips: Consider using wired internet connections (Ethernet) over wireless if facing persistent connectivity issues. Periodically check for software updates; newer versions might contain bug fixes. If the issue is recurrent, consider generating and reviewing FortiClient logs to pinpoint any underlying issues. Share these with the IT department or FortiNet support for a deeper diagnosis. Remember that VPN connections might not work on certain networks (e.g., some public Wi-Fi networks block VPN connections), so always test on a known good network if in doubt.