“UPLOAD_ERR_PARTIAL is given when the mime boundary is not found after the file data. A possibly cause for this is that the upload was cancelled by the user (pressed ESC, etc).”
This may be the reason for error code 3 you are getting..
You can check further at : http://php.net/manual/en/features.file-upload.errors.php
Hope this helps 🙂
Did you check the disk space?? Is there enough disk space on your server to upload the files?
