In the first file you are saving the request_token in the session as oauth_access_token but in the second file you are trying to use the...
"Could Not Authenticate You" means the access_token being used is invalid. You are likely overwriting it at some point with a new request_token.
Assuming you are using the following to post the new tweet. $response = $connection->post('statuses/update', array('status' => 'text to tweet'));...
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