My experience with the Linksys WAP54G v2 access point was that I had to use WPA with AES encryption, not TKIP nor TKIP+AES.

Now I am able to use the 770 with WPA and AES, my preshared key is 15
ASCII characters.

I have had a lot of frustration with finding Linksys PCMCIA cards which have the ability to use AES. I just keep sending them back until I get one that can be upgraded.