This is indeed an error caused solely by the installation of the demo installer, which, according to the forums, has something to do with J version 5.2. Reloading doesn't resolve the problem either. And it only occurs with this template and this J version. I can't do anything else because I keep getting this error message. An update isn't possible either. See screenshot.

I don't think that this is related to the template or the demo installer. These are not error messages, but the pink colour usually shows that the page display is not yet ready. It should disappear when you reload the page. If not, you might have an issue with the .htaccess file on your admin directory.