2nd iPad will only connect to guest network

Hello from a new member needing some help. I've searched and not found this same problem and I apologize if this is in the wrong section. I just got a 2nd iPad 2, this one with AT&T 3G. I'm using a Airport Extreme with an extension via an Airport Express to my garage. All my other devices; Macbook Pro, iMac, 2 iPhone 4's, and the iPad w/o 3G all connect fine with my main network. With the 3G version, the login screen just keeps popping up asking for the network password. I am correctly entering the password and I don't get any error dialog but it keeps asking as if what I'm entering is not correct (100% is correct). If I use my guest network, with the guest network password, everything is fine. I'm also apple to connect to a neighbors unsecured network.

I feel like I'm missing something basic here.

Thanks in advance for anything anyone can offer!