twitter-development-talk

I used to request a user timeline with

/statuses/user_timeline/xtien.xml?count=24

where xtien is a user screen name.
because this doesn't work when the screen name is numeric - Twitter
sees the user name as the id, not the screen name - I changed it to

 /statuses/user_timeline.xml?screen_name=xtien?count=24

However, this gives a 401 response. The request is authenticated. Why
is there a difference between both methods? Or what's wrong in the
second request?