I had the same issue as others in this thread.
I have two installs of Joomla 2.5 on two different dev servers.
Joomla 2.5, K2, JFBConnect, JomSocial, JoomBlog, sh404SEF and more
One versions works, the other does not.
So others don't loose 4 hours like I did, try this.
Kept getting 404 then Component not found errors after Login.
After comparing configs against both sites finally turned off "jomsocialredirect" plugin and SCLogin finally worked as expected.
Did not read the configuration guide and this probably in there. Oh well.
Goodluck.