Why am I being asked to enter a MyData password when I try to login via Google?

Google updated their software such that users no longer login via Google, they login via Google+. ICPSR updated its software as the old login setup ceased to work on April 20, 2015.

When a user logs in on the ICPSR website using Google+ for the first time, it will act as if it was the first time s/he ever tried logging in from Google. The software will match his/her email address to an existing MyData account, and then inform the user that s/he already has a MyData account and prompt him/her to link their Google+ and MyData account. To do so, s/he will need to know his/her MyData password. If s/he doesn't know it, s/he will need to request the password be sent via email, or create a new MyData account.

This is a one-time procedure related to Google discontinuing support of OpenID 2.0.