You should see this error in Magento 2, if you have a theme reference in your database and it’s not within its corresponding directory.
To solve the issue, you should check in your corresponding project design folder (app/design/frontend), and find which difference you have with your database settings. To get the database installed themes you should do:
select * from theme;
Once you get the database themes, you should add the corresponding missing directories, or remove them from the theme database table.
Then remember to clean cache, and the error should be solved.