Jetpack caused fatal error

I assume you had this plugin installed: https://www.ads-software.com/extend/plugins/wickett-twitter-widget/

Since you can’t access your admin panel, you can either delete the whole wickett-twitter-widget directory in wp-content/plugins or delete the whole jetpack directory in wp-content/plugins.

FYI, wickett-twitter-widget plugin already bundled in Jetpack.

Did exactly that–deleted the jetpack directory–after I made this post. Problem resolved, and thanks for your input!

I had the same problem. I have never had the wickett-twitter-widget installed. I did have jetpack installed, and deleting the jetpack directory and re-installing it solved the problem.