Activating the Snapshot causes fatal error

Hi I have a clients site and I wanted to create quick backup before making some changes, uploaded Snapshot Pro as usualy, clicked to activate and it failed with following error and the only way how to solve it was uninstalling (= deleting by FTP) Snapshot. Could you have a look on the issue?

Fatal error: Cannot redeclare comment_exists() (previously declared in D:\Inetpub\webs\2491348_web\www\wp-admin\includes\comment.php:27) in D:\Inetpub\webs\2491348_web\www\wp-admin\includes\comment.php on line 40