Everyone, FYI:
a) This is not a serious issue. It doesn’t affect the performance of the plugin nor of WordPress itself. It will not stop any updates from happening either.
As @laserjobs also said: The relevant function is only called when you update plugins/themes/core and it checks whether you updated the current theme and if so, re-checks whether the theme has a <meta description> tag.
So nothing really major.
b) As @russell Jamieson also said: The issue is caused by a change in WP core in 3.7. They introduced an action hook in 3.6 which WP SEO was using and have changed the way the action is called in 3.7.
c) The issue was first reported by @vickyindo as a bug straight after the 3.7 release. Within hours, I made a patch available.
The pull request is waiting for Yoast to review it, but I very much expect it to be included in the next version.
If you don’t want to wait until then, just apply the changes outlined in this commit.
Oh.. and please do not open any more duplicate bug reports on this issue on GitHub. Duplicates are lazy, not useful and will only be closed.
Anyway, the issue is solved, a patch is available. You can either apply it yourself or wait for the next version of WP SEO to be released.
And @chris M.: that is completely unrelated to this issue – this error has nothing to do with the sitemaps. Please open a separate thread for this and/or if you have more detailed information, file a bug report on GitHub.