I have a new TimeCapsule 2TB and use it as a wireless AP, router, and backup device. The TimeCapsule is directly connected to the DSL modem.
When I turn on the TimeCapsule, everything works fine. But after some hours (maybe 2-4), my MacBook Air no longer finds the TimeCapsule, so backups via TimeMachine fail. Also, AirPort utility no longer finds the TimeCapsule. The strange thing is: the wireless internet connection on my MacBook Air is still perfectly working and I'm also able to mount the TimeCapsule's disk from a Linux machine via Samba. After switching the TimeCapsule off and on again, the AirPort utility finds the TimeCapsule without problems.
Any ideas how to solve or debug this problem? I'm using Mac OS Lion, AirPort utility 5.5.3 and firmware version 7.5.2 of the TimeCapsule.