After upgrade to 6.7.x SGOS you are trying to join Proxy to domain in IWA Direct and when you try to join getting error message "nerr_dcnotfound".

error nerr_dcnotfound

During Domain Controller Selection Mechanism, The ProxySG / ASG appliance (using IWA-Direct)  queries an SRV record in DNS and sends an "LDAP ping" packet to the DCs that it finds. The LDAP ping is a small LDAP-over-UDP packet. In this scenario Domain controller is rejecting UDP pings. 

In LSA debug you can see something like

"TRACE: netlogon - [LWNetSrvPingCLdapThread() lwnet.c:927] Failed CLDAP ping"

Force proxy to use TCP on ldap pings by using the commands below in CLI (use SSH console)

>en
#conf t
#(config)security windows-domains
#(config windows-domains)ldap-ping-protocol tcp
  ok