Prueba imprimir: $_FILES['userfile']['error'] y comparalo con la siguiente lista:
Cita:
UPLOAD_ERR_OK
Value: 0; There is no error, the file uploaded with success.
UPLOAD_ERR_INI_SIZE
Value: 1; The uploaded file exceeds the upload_max_filesize directive in php.ini.
UPLOAD_ERR_FORM_SIZE
Value: 2; The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form.
UPLOAD_ERR_PARTIAL
Value: 3; The uploaded file was only partially uploaded.
UPLOAD_ERR_NO_FILE
Value: 4; No file was uploaded.
UPLOAD_ERR_NO_TMP_DIR
Value: 6; Missing a temporary folder. Introduced in PHP 4.3.10 and PHP 5.0.3.
UPLOAD_ERR_CANT_WRITE
Value: 7; Failed to write file to disk. Introduced in PHP 5.1.0.
UPLOAD_ERR_EXTENSION
Value: 8; File upload stopped by extension. Introduced in PHP 5.2.0.
http://www.php.net/manual/en/feature...oad.errors.php
Saludos.