Thanks for the tip.
I did follow your instruction and downgraded my Airport Utility 6.3 to 6.2 on my Mac. But the Airport Extreme firmware is still 7.6.3
I guess I need to downgrade my AE firmware, but I don't know how.
Any advice would be much appreciated, since I have been spending hours to firgure this out.
MacBook Pro with Retina display, OS X Mountain Lion (10.8.3), rMBP 15, TWC high speed internet