I have the same problem under Squeeze with nm-applet (GNOME-frontend).
I use the maximum WPA key length (64 characters, which works under
other distributions) but the dialog does not accept it ("connect" button
If I shorten the key by three characters (to 61 characters), the button
is enabled again (but the key is of course wrong then).
The key consists of ASCII characters only (upper and lower case, digits).
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