Hello I have been having the same problem to, it seems twitter is updating it’s API and everyone has been left in the dark. As far as I can tell these forums aren’t moderated so I found a separate solution.
If you use the following plugin - http://wordpress.org/plugins/really-simple-twitter-feed-widget/
It takes a little longer to set up but it should work just as well if not better. Also it is styled the same as the original.
Hope this helps!