Hide Forgot
I regularly connect to a hidden wireless network. This is set up as an automatic connection but can take a very long time to connect without prompting. Hence I normally try to make the connection manually by selecting "Connect to Hidden Wireless Network ..." from the drop down menu from the icon and selecting the Connection from the list in the subsequent dialog box. Then I used to be able to select the Connect button, however recently this button has remained greyed out so I can no longer use this method. I wonder if this is related to Password length checking, which might be incorrectly disabling the Connect button in this case because there is no password in the dialog box.
I have the same problem: I use NetworkManager to connect to a hidden wireless network (WPA2 security). Under Fedora 11 the connection was established without a problem. Updated from Fedora 11 to Fedora 12 Beta (upgrade with DVD). NetworkManager does not autoconnect to the hidden network. When I manually select "Connect to Hidden Wireless Network ..." and select the connection profile from the list, all GUI elements except the "Cancel" Button are greyed out. I can provide additional information (hardware specs or screenshots) if needed.
Fixed in http://koji.fedoraproject.org/koji/taskinfo?taskID=1762133, which was pulled into Fedora 12 right after the beta went out. If you 'yum update NetworkManager*', it should give you that build, and it should fix your problem.