You need to use the plugin WP Rollback and rollback to version 2.3.5 to solve this issue. There are thousands of people having problems and there is no fix at the moment, other than going back to the latest working version of Yoast SEO which is the one I recommended above.
Right now the only solution is to stay on 2.3.5. There are thousands of people having problems with the plugin at the moment and no solutions other than what you just did.