Cannot connect to Wi-Fi (The Wi-Fi network "network name" requires a WPA2 password)

I would recommend removing the wireless network from your preferred networks. You can do this by going to your network preferences. As follows:

Open Network Preferences > Select your Wi-Fi connection > Advanced.

Select the network from the list on the first Wi-Fi Tab and hit the [-] key then click OK.

Once you have done this, click Apply on the next screen.

Next you want to remove the password from your keychain to make sure its gone. So open up Keychain Access Application.

Search for the wireless network name. Select the network name and hit delete key. Click the delete prompt to be sure.

Close Keychain access and retry connecting to the wireless. This should have removed all traces of the wireless network from your computer and allow you to try it again.