Cisco Wireless :: AP Does Not Join The 5508 WLC When NAT Is Configured

A customer runs a 5508 WLC for quit a while. several dozens AP's are spread all over Europe an run just fine. All the AP's have a VPN based connection over an MPLS service provider, so we are using 10.x.x.x addresses only. We have upgraded to release 7.2.111.3 to support OEAP 600 and we have configured NAT in the Firewall as well a policy to support the home office AP. Everything works fine until the switch where the WLC was attached to crushed. From this moment on, all internal AP's ar no longer able to register at the WLC. A log at the console port on an AP shows that it tries to access the external (NAT) IP address. We had to remove the NAT flag to support the internal AP's.