Hi, thanks for the swift reply. I deactivated all plugins, the notice remained. I actived a default theme and the notice dissapeared…. To be 100% sure, I installed a new empty site, with a new database. No notice with the default themes. Installed and activated the Ultimate Pro theme and there was the notice again…
Since you can only see the notice with debugging on, I’ve set the debugging off and everything looks okay. In the meanwhile, I think you might have a look at the theme to find out why that notice showed up with your theme.