Check your response headers from twitter for:
X-Warning: Invalid OAuth credentials detected.
based on:
Ensure you inspect the headers returned when requesting methods which
do not require authentication. If the request you make includes
invalid OAuth information the API will do one of two things:
For methods which require authentication, the API will return an error
response with more information about the error. For example an HTTP
401 error with the response body Could not authenticate with OAuth.
For methods which can be requested unauthenticated, the API will
process the request as if authentication had not been used. This means
the request will count against the unauthenticated rate limit. If this
has happened the API will include the following header in it's
response: X-Warning: Invalid OAuth credentials detected.
I suspect your problem has more to do with an Oauth mismatch then anything else. the Obtaining access tokens page may be of some help.