Exchange 2010 CAS Unicast NLB being blocked by Cisco NAC

My wireless is using Cisco NAC and the connection to the NLB virtual IP is being filtered out causing Outlook users are not able to access to the Exchange server.

All connection from LAN is working as there is no firewall in between.
The NLB was setup using unicast. What could have cause this.

May I know how does NLB actually works. Inbound connection is via Virtual IP and the outbound connection is via physical IP? Is it why the NAC is blocking the traffic?

Thanks.