[Plugin: Google Drive for WordPress] Http 500 error when clicking on time backup

The setting up process is quite smooth. But when I want to perform the backup, it said,

HTTP Error 500 (Internal Server Error): An unexpected condition was encountered while the server was attempting to fulfill the request.
wp-admin/admin.php?page=backup_to_google&action=update&update=1. It may be down for maintenance or configured incorrectly.

The server env:
IIS6/PHP5.2.8/MYSQL5.1.34/WP3.3.2 and WP3.4.1
The client side:
Chrome/OS X
I guess if there’s any env setting not match the requirement?
Please kindly give some advices
Thank you.

https://www.ads-software.com/extend/plugins/wp-google-drive/