tapster/omniauth-meetup — pull request #4 by russ (2013-06-27 19:48:34+00:00)
Title: Meetup OAuth2 change

Meetup has made a change to their OAuth implementation. It returns
an error when using two forms of authentication.

You can refer to this url for a little history on the problem.
https://groups.google.com/forum/?fromgroups=#!topic/meetup-api/Ox1NG2mplkU