Since PHP 4.2.0, PHP returns an appropriate error code along with the
file array. The error code can be found in the
error segment of the file array that is created
during the file upload by PHP. In other words, the error might be
found in $_FILES['userfile']['error'].
Value: 0; There is no error, the file uploaded with success.
Value: 1; The uploaded file exceeds the
directive in php.ini.
Value: 2; The uploaded file exceeds the MAX_FILE_SIZE
directive that was specified in the HTML form.
Value: 3; The uploaded file was only partially uploaded.
Value: 4; No file was uploaded.
Value: 6; Missing a temporary folder. Introduced in PHP 4.3.10 and PHP
Value: 7; Failed to write file to disk. Introduced in PHP 5.1.0.
These became PHP constants in PHP 4.3.0.