Native vpn for mac failing to connect with nat-t error

Hello everyone,

I hope you can help me with this, as I'm breaking my head for days without any results.

I'm unable to connect to fortigate vpn from mac devices using native vpn

This happened after the fortios upgrade to 6.0.5 version.

Here is the error I'm getting from debug output:

ike 0:VPN-AM:344021: unsupported NAT-T version draft-ietf-ipsec-nat-t-ike-04 ike 0:VPN-AM:344021: unsupported NAT-T version draft-ietf-ipsec-nat-t-ike-05 ike 0:VPN-AM:344021: unsupported NAT-T version draft-ietf-ipsec-nat-t-ike-06 ike 0:VPN-AM:344021: unsupported NAT-T version draft-ietf-ipsec-nat-t-ike-07 ike 0:VPN-AM:344021: unsupported NAT-T version draft-ietf-ipsec-nat-t-ike-08 ike 0:VPN-AM:344021: selected NAT-T version: RFC 3947

and here the error I'm geting on iMac:

The negotiation with the vpn server failed. Verify the server address and try reconnecting.

p.s 

The server address is correct and the PSK too.

Thanks in advance