This value controls which OSI operating mode Access Server runs on.
Depending on your configuration, sometimes changing the operating mode may break your connectivity permanently. This especially is the case when changing from OSI Layer 3 to OSI Layer 2 operating mode.

To restore connectivity, you can try changing the operating mode manually from the CLI.
To do so, execute the following commands:
/usr/local/openvpn_as/scripts/confdba -mk vpn.general.osi_layer -v 'opMode'
where opMode is 2 for Layer 2, and 3 for Layer 3.

For example, to change your operating mode to Layer 3, use the follow command:
/usr/local/openvpn_as/scripts/confdba -mk vpn.general.osi_layer -v 3
After that, restart the OpenVPN Access Server completely by executing:
/etc/init.d/openvpnas restart