Cannot edit entries after Redactor 2.0.1 upgrade
I have an unfair advantage since I got to look at your logs from your support ticket, but here's the error from the logs:


  [error][yii\base\InvalidConfigException] yii\base\InvalidConfigException: Redactor plugin not found: source


If you look at the Changelog for Redactor 2.0.0, you'll see the "Source" plugin is no longer needed.

The upgrade from Redactor 1.x to 2.0 should have tried to clean up any craft/config/redactor/*.json config files you might have removing references to the "Source" plugin, but something might have went wrong (permission errors are the most common cause of that).

Regardless, if you update those Redactor config files, the error should go away.