Ensure that the Google App is correctly configured and you don't receive an error message when reaching the Google permission page. After that you must be redirected back to your site for the login.
Double check that the IFBL login module is assigned to the home page too, otherwise the login won't work. It's reported in the PDF docs and at this FAQ
http://storejextensions.org/faq/why-the-social-authentication-does-not-produce-any-effect-and-login.html
If these are not the problems i have no other clue at the moment.
