Here is a very simple fix I found that may help. I did the trick for me.
As noted here the default plug-n-play configuration for OpenVPN Access Server doesn’t work.
The problem is with the network config for uci. There are no default firewall rules for handling vpn traffic. Without them the turtle won’t pass traffic from the vpn interface to the br-lan interface.
You can correct this by adding the following to /etc/config/firewall on the turtle. Put it in around line 26, before the lines that start with config rule:
option name 'vpn'
list network 'vpn'
option input ACCEPT
option output ACCEPT
option forward REJECT
option src vpn
option dest wan
After doing so, run the following:
This will bounce the interfaces and reset the firewall rules. With these instructions in place, you’ll be able to reach the network on the far side of the turtle.
NOTE (2016/09/06): An earlier version of this article (and a corresponding forum post) mistakenly configured the lan interface instead of the wan interface. On the LAN Turtle the RJ45 port is wan.