This policy setting allows you to specify if the Diffie-Hellman Group 14 protocol can be used by the Internet Key Exchange ...

"This policy setting allows you to specify if the Diffie-Hellman Group 14 protocol can be used by the Internet Key Exchange (IKE) protocol during Mobile VPN key exchange negotiations.  If you enable this setting, the Mobile VPN  can use Diffie-Hellman Group 14 key exchange.  If you disable this setting, the Mobile VPN  cannot use Diffie-Hellman Group 14 key exchange.  If you do not define this policy setting, the default behavior is to allow all supported groups.  Note: If all Diffie-Hellman groups are explicitly not allowed, the Mobile VPN fails."