Got this message from server after clicking "Update CDN data" :
Unexpected Error
<b>Fatal error</b>: Allowed memory size of 41943040 bytes exhausted (tried to allocate 20 bytes) in <b>.../wp-content/plugins/jsdelivr-wordpress-cdn-plugin/jsdelivr.php</b> on line <b>639</b>
http://wordpress.org/extend/plugins/jsdelivr-wordpress-cdn-plugin/