Error when activating WHMCS plugin

Hi,

I am getting an error when activating this plugin.
This is the error:
Warning: chmod() [function.chmod]: Operation not permitted in /home/webshop/domains/webshopservice.nl/public_html/wp-content/plugins/whmcs-wordpress-integration/whmcs-integration.php on line 359

Warning: chmod() [function.chmod]: Operation not permitted in /home/webshop/domains/webshopservice.nl/public_html/wp-content/plugins/whmcs-wordpress-integration/whmcs-integration.php on line 360