OpenVPN fail

After a period didnt use OpenVPN, I come back for it again.
at start i try for start the GUI and connect. but keep fail for errcode=31
and show some permission message. I check around the internal to solve it, but still fail.
i thought it was cause by
- i add domain to server
- didnt update virtualbox (i thought the version not sync to host)
- windows update

but i keep on checking on permission.
and check on openvpn server.

what i do:
- stop star service
- restart server and client
- reinstall ( and with ltest version)

but still fail. then i try on another cert which give me another error. (but both cert is same setting)
make me blur why same setting may cause different error.
finally, i get it.
i start service from clinet side which shouldnt start.
cause once u start the service, it will use up TAP network, and GUI not able to use it.
Actaully not openvpn fail, Is me fail.