When using a FTP server for storage, you try to upload a large file and it fails. Smaller files work ok.
This is an issue with PHP not having access to enough memory to process the request. To fix it add this line at the end of your _config.inc.php file (in the script root folder):
You should set this limit to the maximum permitted filesize you're allowing on upload. Note: 2048M may be the maximum on a 32 bit system.