Using API to search tweets


I am struggling to make my application to work with the new API. I keep getting errors: Bad Authentication data code 215 or http error 400. Can’t seem to work out where exactly the authentication is failing!! I have tried various combinations such as<User_id>&screen_name=&oauth_consumer_key=&oauth_signature_method=HMAC-SHA1&oauth_token=<Access_token>&oauth_signature=<Access_token_secret>

Any idea please?