FortiClient VPN connection failure inside FortiWiFi 30E

A user with a Windows 10 Pro notebook can access the Fortinet VPN server in data center from home.

In office, there is a FortiWiFi 30E.  She gets the following error message in reaching 80%.

"Warning 

Unable to establish the VPN connection.

The VPN server may be unreachable. (-14).

Please help!