If you have a mixture of strings starting with @ (at character) and files in CURLOPT_POSTFIELDS you have a problem (such as posting a tweet with attached media) because curl tries to interpret anything starting with @ as a file.

<?php

$postfields = array(
    'upload_file' => '@file_to_upload.png',
    'upload_text' => '@text_to_upload'
);

$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, 'http://example.com/upload-test');
curl_setopt($curl, CURLOPT_POSTFIELDS, $postfields);
curl_exec($curl);
curl_close($curl);

?>

To get around this, prepend the text string with the NULL character like so:

<?php
    $postfields = array(
        'upload_file' => '@file_to_upload.png',
        'upload_text' => sprintf("\0%s", '@text_to_upload')
    );
?>

Original source: http://bit.ly/AntMle