There are many possible reasons Concentrator can fail to generate the self-signed Secure Socket Layer (SSL) certificates for an interface.
One of the more common reasons is that Concentrator is configured for load balancing. Concentrator can fail to generate a certificate even if there are no other certificates.
In order to resolve this issue:
Remove load balancing, and try to regenerate the certificate.
In order to disable load balancing on the VPN 3000 series Concentrator: