I too just came across this error. It works fine on one site, but a copy of that site that I am working on has the error. I don’t have the W3 plugin or anything like it.
The error creates a bar about the height of my Top Nav Bar aboce said bar with the error code behind the semi-transparent bar. The setting of this site are all the same as the site it currently works on, so not sure what’s up. Jus thought I would add my voice to the discussion ??
Edit: Now it also shows on the dashboard if that helps with anything. Also, I would be more than happy to have you email me the new code before the update to repair it myself if that offer is available.
Love the plugin btw. Sooooo easy and customizable. Kudos.