We've got a Cisco 1230AG access point with Broadcom BCM4309 mini pci wireless cards. We're using 802.11a with 128 bit WEP.
Our Broadcom clients are being disconnect "out of nowhere", and a trace shows the access point sending deauthentication frames saying "Previous authentication no longer valid".
We've seen this with other vendor's access points as well, so we think the problem might be the client. The access point log also shows the deauthentication, so I'm pretty sure the frames are originating from there (and not an attack).
Do clients need to renew their authentication, or why would an access point send them a deauthentication?