What worked for me in similar situation:

1. Go to File Editor, rename wp-content/plugins folder to whatever
   
2. This allowed me to log in at /wp-admin
   
3. Go to updates and reinstall wordpress even if it is most recent
   
4. Go to plugins page, it will show you plugins are missing files
   
5. Then go back to file editor, rename folder back to "plugins"
   
6. Update all plugins
   
   

error should disappear