Let me do better than posting links. Dont bother trying to reconfig yourself. This is an apple published fix, right here in apple support folks.
Please stop being confused and searching for answers. It's spelled out in detail, apple would just rather you not be able to find the fix, presumably because the offering of the solution reveals that THERE IS INDEED A PROBLEM!!
Here's the link to the solution found here in apple support ... http://support.apple.com/kb/HT5656
A could more times for good luck. http://support.apple.com/kb/HT5656. http://support.apple.com/kb/HT5656. Next i will post the actual text of the release.
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AirPort base station: IPv6 Tunnel Error after installing firmware 7.6.3 in router/NAT mode
Learn about AirPort Utility pop-over error: IPv6 Tunnel Error.
Important: Follow these instructions only if your AirPort base station is operating in DHCP and NAT mode. Do not follow these steps if your AirPort base station is operating in Bridge mode. Check your AirPort base station Router mode setting by selecting the Network tab. The Router Mode is the first setting.
AirPort firmware 7.6.3 requires that all fields for IPv6 Manual Tunnel mode be completely filled in and contain valid entries (Note: This does not apply to IPv6 Automatic Tunnel mode). If you were using this mode prior to firmware 7.6.3 and settings for IPv6 manual Tunnel mode were incomplete or missing, the base station will flash amber, and AirPort Utility will show a pop-over error: IPv6 Tunnel Error.
Selecting the error from the AirPort Utility pop-up will show the following: "There was an error with the IPv6 tunnel endpoint. Wait for the service to be restored and try again. Contact your service provider if the problem persists."