Google Bots can be one of the annoying things for people creating a Social Network, Google will and can through you alot of error relating to redirect rules within the Social Engine framework.
This is a easy fix for this which is deny any bots from accessing the Redirect url login scripting.
If you open your Robots.txt file with note pad or another text editor and add this line to the Robot File.
User-agent: * Disallow: /login/return_url/
Save the file and reupload it to your root folder, this should now stop any robots from accessing a return url.