Me too. I received the same message today (with the exception of the line number).
I’ll answer the three questions in the previous comment:
1) No, I’m not able to use the plugin. Going to any admin page in the site displays that error.
2) Have not had an opportunity to activate Cloner with no other plugins due to inability to get to admin pages. (I just updated to the current version of NS Cloner prior to network-activating it, and I believe WP is updated to current version too.)
3) No.