You might encounter this issue when your server disk is full:
CPage error in CMain/locateChild:
To resolve this, you just need to free up disk space on your OpenVPN Access Server node and restart the openvpnas service again.
Try to remove old files or openvpnas.log from the /var/log/ folder and then perform:
Then check available space again:
Also, you can configure log rotation as described here: Setting up log rotation for /var/log/openvpnas.log.*