Thanks everyone.
Yes, making the change to capabilities.php allowed me to complete installation.
But the new version doesn’t allow important features of my theme to be displayed properly. (Featured images from media don’t display in the posts and my site’s front page doesn’t show the images that link to the posts, just empty squares). My theme is Autofocus.
Since I overwrote my backup (I still have another from ten months and a dozen posts ago on my local computer), I’m going to try to manually upgrade to 3.61 by replacing admin and includes folders and overwriting content. And replacing corresponding files in root. I’m prepared to restore my database with phpMyAdmin.
Is there anything that I should be worried about?
Thanks in advance for your help.