GET statuses/timeline suddenly rejecting my requests


I have written code that gets a request token, authenticates the user, obtains the access token and secret access token, and then gets the user’s tweets. I last ran this code in late February 2015 and it worked perfectly. However, I tried it today and now I’m getting a 401 when I try to get the user’s tweets by sending a GET request to statuses/timeline. I’m working in Trinity College Dublin and am behind their proxy. Could that be a cause of the problem?