If you are using Windows Vista, and WPA2, WPA2 does not work. Once in a while it will connect, but most of the time it will tell you your key is incorrect, even when you supply the correct password.
To fix this, you can change your wireless AP to allow access for both WPA-TKIP and WPA2-AES. Then, you need to manually configure the network in Vista, because if you view networks, and try to connect, it will continue to try WPA2.
To do this, go to:
Start > Connect to..
- or -
Start > Control Panel > Network & Internet > Connect to a network (under Network & Sharing Center)
Click the link that says "Set up a connection or network"
Select "Manually connect to a wireless network" > Next
Select WPA-Personal for Security Type
Select TKIP for Encryption Type
Enter your appropriate Network Name and Security Key/ Passphrase
You should get a dialog that says "Succesfully added <network name>
Click Connect to
and you should be set.
This issue seems to be resolved in Windows 7.