1) That's by design. NodeXL does not get installed in the usual "Program Files" folder. (NodeXL is a ClickOnce application that gets installed in the ClickOnce cache.)
2) Please provide more details. The usual sequence is this: You select "I have a Twitter account, but I have not yet authorized NodeXL to use my account...", then you're taken to a Twitter web page where you enter your account information, then Twitter gives you a PIN, then you enter the PIN in NodeXL, and then you get the network. At what point in this sequence did you get the "401 (unauthorized)" message?
3) If you want a network involving an individual Twitter user, go to NodeXL, Data, Import, From Twitter Users Network.
-- Tony
2) Please provide more details. The usual sequence is this: You select "I have a Twitter account, but I have not yet authorized NodeXL to use my account...", then you're taken to a Twitter web page where you enter your account information, then Twitter gives you a PIN, then you enter the PIN in NodeXL, and then you get the network. At what point in this sequence did you get the "401 (unauthorized)" message?
3) If you want a network involving an individual Twitter user, go to NodeXL, Data, Import, From Twitter Users Network.
-- Tony