AC68 -Merlin 378.56 beta2- OpenVPN can't start

Hi, just registered and have a question on starting OpenVPN server on my AC68 with 378.56 beta 2.
If I run OpenVPN with Authorization Mode set to TLS, it runs fine.

I also want to run a OpenVPN with Authorization Mode set to Static Key, it appears the server can not be started. below is the router's general log. I am not sure if I am running some wrong setting or what.

Please take a look. Thanks.

Router log:
Oct 22 21:34:00 openvpn[1406]: Socket Buffers: R=[87380->87380] S=[16384->16384]...

AC68 -Merlin 378.56 beta2- OpenVPN can't start