I received this advice on a previous post, but it was closed before I was able to respond, “I suggest that you delete the cornerstone plugin folder by using your file manager or FTP then go to this directory wp-content/plugins then look for the cornerstone folder and delete it. Once you are done deleting the folder then try to reinstall the cornerstone plugin again in your dashboard.”
I deleted the plugin successfully and am no longer receiving an error message which I thought solved the issue. HOWEVER, now, I do not see the Cornerstone plugin listed in the left menu bar (as the theme documentation says that it should be). I only see it listed when I visit the “plugins” option, listed with a number of other plugins.
In addition to that problem, I now have a little “+” in the top right of my website. I assume this is something to do with the plugin. However, when I click it, all that happens is a plain white bar appears with nothing else. (The photo attachment shows the before and after.)