Sorry that no one has helped you out prior to now.
I've just encountered pretty much the same issue today with a site and it's probably been going on for ages, but the client hadn't logged in the way I was doing so today.
My problem was that when logging in on a page that was not the home page, OpenSEF would add an extra / into the url, so you'd have
www.site.com//redirection which then gave a Page does not exist error.
CB_Login module was set to go to the page that I logged in from.
Going through the OpenSEF settings, in the Features area, "Generate Absolute URLS" was off. Turning this back on removed the error, so now users can successfully login when not on the home page, and the URL is written correctly.
Hope that helps.