Mac OS X v10.6: Exclamation icon displayed in Wi-Fi menu after entering a WEP password
When you attempt to connect to a Wi-Fi network that requires a WEP password by using the correct password, you may not be able to connect to the Internet or other Wi-Fi devices on the same network.
You may note that the Wi-Fi Menu Extra shows a Wi-Fi icon with an exclamation point () and that your computer has a self-assigned link local address (such as 169.254.x.x). The Wi-Fi menu may also indicate that there is an "Alert: No Internet connection...".
This may occur if the password isn't provided in the format required by the network.
To learn how to adjust the format of the password so that it will be accepted, see this article: Joining an encrypted wireless network.