Capsule 5 GHz lost after upgrade to 7.4.1

Hi all,

I just upgraded my (old) Time Capsule to firmware 7.4.1 this morning. After upgrading
it seemed that my wireless network was not working anymore ( I had my capsule creating
a 802.11n only (5GHz) network). I could not see the network from the macs that previously
worked, nor could I connect to that network.

Resetting . rebooting both the capsule and the macs did not resolve. also reconfiguring the
capule brought no relief. All other functions of the capsule are OK.

When I switch back to 2.4 GHz (802.11n only (2.4GHz)) I saw the network again, and could
use it. So: only 5GHz does not seem to work properly after firmware upgrade ...

Any ideas from the community how to fix this ?
Is there a way to revert to the old firmware, as I need 5 GHz, as 2.4 is overcrowded here.

Rudi