I just bought an Apple TV last night. I have it sitting directly underneath my Airport Express. I have 2 wifi connections on my Airport, one for my stuff and one for guests.
When I list the wifi connections in my Apple TV it sees both, however when I try to connect to either I get this message:
There was a problem connecting to the network.
Check your settings and try again. (-3906)
I tried with a bad password just to compare the difference and I get this message:
There was a problem connecting to the network.
The Wi-Fi password you entered is not correct. Try again. (-100)
So it can see it, and tell it is the correct password; but it will not connect.
My MBP, MPA, Android phone, Xbox, and guests' windows laptops have all connected to this airport without any problems.
It does work if I connect the Apple TV to the Airport via ethernet.
Best Answer
I have 2 apple tv’s. One wouldn’t work anymore. I went to Utilities, Airport Utilities and noticed there was a newer version available. Once I installed the newer version my apple TV finally worked. I don’t know if this will help anyone else, but it did the trick for me.