Plug it in via ethernet and redo the setup.
Use names for the TC and wireless that are short, no spaces pure alphanumeric.
Use WPA2 Personal security with 8-12 character pure alphanumeric key.
Fix the wireless channel for 2.4ghz.. try 1, 6, 11 in turn.. these are the only non overlapping channels.
I would also suggest a different name for 5ghz at least until this is fixed.
Absolutely use 5.6 utility..
v6 utility is toyland version.
If you updated to lion 10.7.5 make sure it is latest or apply the supplement.
Apple totally bungled TM in the first effort.