My Time Capsule's 5GHz network does not appear as a network any longer. Airport utility is 5.5.3 and iMAC is 10.7.1 The TC appears to be configured correctly in the utility screen.

By default the 5GHz network and the 2.4GHz network are broadcast with the same SSID (wifi network name). So while it only appears in your wifi list as a single network, it is actually being broadcast on both frequencies. Hardware that is compatible with the 5GHz band will connect at that frequency and hardware that is only compatible with the 2.4GHz band will connect at that frequency. On your iMac you can check what freqency it is connecting at and the speed of the connection by holding the option key on your keyboard and clicking on the airport icon in the top right of your screen.

Wish some Apple folks would chime in...

Apple is not here. Even if they might rarely monitor these boards, they will not respond. We're all users, just like you.

Suggest that you open Macintosh HD > Applications > Utiltiies > AirPort Utility

Click Manual Setup

Click the Wireless tab below the icons

Click the Wireless Options button

Check one more time to see if you still have the 5 GHz Name option enabled. If not, enter a check mark and click Update to save the new settings.

If 5 GHz is enabled, temporarily disable the setting and Update. Then go back in and enable the setting again.

If you still cannot "see" the network from any device, about all that you can do at this point is reset the Time Capsule back to factory defaults and try the configuration again to see if it will "take". Lion is causing some strange issues, and this may be another.

If this is not successful, then it's time to contact Apple support or arrange a visit to an Apple store to let them take a look

Good luck. Keep us posted on your progress. I assume that you have done all the other obvious stuff like a complete power cycle of the entire network?

The "5GHz Network Name" option does not enable the 5GHz network - broadcasting on the 5GHz frequency is always enabled on all the dual-band Extreme base stations. Clicking that box simply allows you to give the 5GHz network a different name than the 2.4GHz network. By default it appends "5GHz" to the end of your standard SSID making them appear in your Airport menu as "xyz" and "xyz (5GHz)".

But what you are saying is even though you have done this, and given your 5GHz network a different SSID it doesn't show up on any of your devices?