Export module using Module Management doesn't work

If you are using Vtiger 6.5.x, please roll back to vtiger 6.4 Zip library from : http://code.vtiger.com/vtiger/vtigercrm/raw/6.4.0/vtlib/thirdparty/dZip.inc.php

Then in /vtlib/Vtiger/Zip.php replace this:
$zipfilesize = $disk_file_size + ($disk_file_size % 1024);
With this:
$zipfilesize = $disk_file_size;