One of our small business clients' networks has SBS 2003 (which is the DHCP server), a Cisco Catalyst 2960 Ethernet switch, and some wireless clients--some Dell (and a Sony) laptops and a Silex CWG-6700 wireless/USB print server.
Regardless of which wireless access point we use (we've tried both a cheap Linksys WAP54G and a more robust Cisco AP1121G), when security is configured to use WPA, none of the wireless clients can consistently maintain or even reliably obtain a wireless connection to the network. The wireless net is detected, but often no IP address can be acquired ("Limited or no connectivity"--as though the encryption key wasn't entered correctly, but we know it was, in part 'cuz the issue is intermittent). Even after an IP and good connection have been acquired, they are randomly lost.
HOWEVER, if we use WEP for security, all problems disappear; all clients obtain IPs with no problem and maintain good, uninterrupted network connectivity, rock-solid.
I've done my share of Googling and understand that WPA involves more complicated communication than WEP and can be tricky, but I haven't found anything that gave me an "aha!" moment or revealed some basic thing that I don't understand about how to use WPA. All of our wireless devices and adapters are relatively new, with up-to-date drivers installed; they can all do WPA. And they're various vendors' devices--Dell, Sony, Linksys, Cisco, Silex--all having exactly the same problems when WPA is used, all working perfectly when WEP is used.
I did find some suggestions, which I haven't tried yet:
--Use AES instead of TKIP
--Use fewer/more characters in WPA key
--Let WAP device auto-generate WPA key (FWIW, the WPA key we were using was a simple ten-character sting of numbers.)
Can anyone explain why we can't get a stable wireless network using WPA, and what I should do to make it work properly?