Make sure the filesize isn't exceeding the settings in your php.ini or the file will just fail to upload.
upload_max_filesize integer
The maximum size of an uploaded file.
When an integer is used, the value is measured in bytes. Shorthand notation, as described in this FAQ, may also be used.
AND if muliple:
max_file_uploads integer
The maximum number of files allowed to be uploaded simultaneously. Starting with PHP 5.3.4, upload fields left blank on submission do not count towards this limit.