Hi Jonny!
I was having the same problem as you were but i found that i could fix it by making this change to the /etc/radius.conf file.
(This is my /etc/radius.conf on my testVM)
acct 192.168.1.1:1892 *passhere*
auth 192.168.1.1:1892 *passhere*
You will see that i just changed the file to add the port for the radius server. I found that without this the openvpn server was never even talking to my radius server (found after a LOT of log hunting and debugging). Try making that change then rebooting your box.. It should hopfully work at that point. If not post back here or PM me and ill try and help you out with it =)
-Eureka
Here is my log:
Jan 12 23:25:52 openvpn[343]: TUN/TAP device /dev/tun0 opened
Jan 12 23:25:52 openvpn[343]: /sbin/ifconfig tun0 10.87.99.1 10.87.99.2 mtu 1500 netmask 255.255.255.255 up
Jan 12 23:25:52 openvpn[343]: /etc/rc.filter_configure tun0 1500 1543 10.87.99.1 10.87.99.2 init
Jan 12 23:25:55 openvpn[343]: Listening for incoming TCP connection on [undef]:443
Jan 12 23:25:55 openvpn[343]: TCPv4_SERVER link local (bound): [undef]:443
Jan 12 23:25:55 openvpn[343]: TCPv4_SERVER link remote: [undef]
Jan 12 23:25:55 openvpn[343]: Initialization Sequence Completed
Jan 12 23:26:14 openvpn[343]: Re-using SSL/TLS context
Jan 12 23:26:14 openvpn[343]: TCP connection established with xx.xx.145.118:3680
Jan 12 23:26:14 openvpn[343]: TCPv4_SERVER link local: [undef]
Jan 12 23:26:14 openvpn[343]: TCPv4_SERVER link remote: xx.xx.145.118:3680
Jan 12 23:26:27 openvpn[1253]: rad_send_request: No valid RADIUS responses received
Jan 12 23:26:27 openvpn[343]: xx.xx.145.118:3680 PLUGIN_CALL: plugin function PLUGIN_AUTH_USER_PASS_VERIFY failed with status 1: /usr/local/lib/openvpn-auth-pam.so
Jan 12 23:26:27 openvpn[343]: xx.xx.145.118:3680 TLS Auth Error: Auth Username/Password verification failed for peer
Jan 12 23:26:27 openvpn[343]: xx.xx.145.118:3680 [client1] Peer Connection Initiated with xx.xx.145.118:3680
Jan 12 23:26:28 openvpn[343]: xx.xx.145.118:3680 Connection reset, restarting
I have a feeling that my radius server isn't running. I did telnet 10.87.0.1 1892 and it didn't connect (usually if something is listening it comes back with something at least...)