RADIUS over IPSEC Not working

Hi there!

I have a set of RADIUS servers that are up and running and are accessible by the Fortigate that it is directly connected to.  But, when I try and use one of the RADIUS servers as a secondary IP through the IPSEC VPN I always get the message "Can't Contact Radius Server".

I've looked and found very little information on this.

Can someone provide some guidance on overcoming this obstacle.

Thanks in advance.