try putting this in user.config:
<add key="OpenIdRpxUseOldImplementation" value="true" />
the only thing I know of related to this that changed is that the default value changed from true to false, if you put this in user.config then touch Web.config it should go back to the old implementation and hopefully that will get you into the site.
Once you login go to Site Settings > Security > OpenID and click the button to setup Janrain
After re-configuring Janrain try removing the above from user.config file and touch Web.config file again, then verify that you can still login