Troubleshooting Tip: 'Unable to establish the VPN connection. The VPN server may be unreachable (-20101)'

[hjhajj]

Description	This article describes how to resolve the issue of SSL Connection error 'Unable to establish the VPN connection. The VPN server may be unreachable (-20101)' and the connection fails at around 91%.
Scope	SSL VPN, FortiGate, FortiClient, Windows 10.
Solution	In case the SSL VPN Connection fails at almost 91% and the error is 'Unable to establish the VPN connection. The VPN server may be unreachable (-20101)', follow these steps: Check if it is possible to access the SSL VPN tunnel through web-mode: SSL VPN web mode for remote user If the SSL VPN Connection is successful using web mode: In most cases, the root cause is that the Windows client machine is being utilized consistently for a long time without restart/closure, OR the machine slept/resumed some number of times: Restart FortiSSLVPN demon (Services.MSC). Restart FortiSSLVPN Client. If the issue persists, check if the FortiClient is a trial/free version. Try re-installing the FortiClient and test the connection. Most probably, it should work. If it still does not work, try re-installing Windows on the client machine. If the issue is still not resolved, it is recommended to use the upgraded version of FortiClient.