Hi everyody !
I also had issues installing 7.6 firmware on a last generation 2TB Time Capsule and Airport Express.
After this upgrade all the access control settings using mac adresses I previously made were changed,
and every attempt I would make to put back the right setting on one device this setting was automatically duplicated on the other ...
I downgraded to 7.5.2 Firmware and all turned back to normal.
To-night I saw there was an upgrade for Airport Utility (with graphic interface like the airport app for Iphone & Ipad)
I Downloaded it and realising there was also a new 7.6.1 Firmware release,
I installed it to, thinking the glitch would be solved ...
... Unfortunatly not ! just the same problem with mac adresses access control settings duplicating from one device to the other !
The big point is that with previous Airport Utility you had an option in the edit menu to downgrade to older firmware releases / With the new graphic Airport Utility it's no more available ! So take care !
Lucky me I had done the airport utility upgrade only on my MacBook Air and not on the Imac.
so I could easily downgrade the TC and Airport Express(s) from the old Airport Utility from my Imac and everything turned back fine.
The bad trip was when I wanted to get back to the old non graphic Airport Utility on my MacBook Air,
I tried first to download previous release from Apple web site and it would install successfully,
but would never replace the new one.
The only solution I found was to restore my entire system from Time Capsule backup ....
Good training anyway, it's working fine with the inner Lion rescue boot drive.
In fact I was in great hope the new TC Firmware would solve a bad issue we are many to be struggling with for weeks : The Poblem with Time Machine not Finding Time Capsule sparsbundle since Mac Os Lion 10.7.2 release.
and that is still unsolved despite all the posts, bug reports and calls to Apple Care hot lines ...
I am a bit desappointed as it seems to me Back-Up is a key point.
Jean.
You can get a look to :
1) Re: time machine looking backup disk
2) Re: "Time Machine could not complete the backup" after 10.7.2 update