Originally Posted by carolus
Which login script? Something in /etc/gdm3? What plugins? (For a default Wheezy installation.)
GDM is the greeter presented when you log in. Type your user name, hit enter. Underneath the password field should
be a "Session" drop down. Click it, then select "GNOME Classic" then enter your password.
Edit: GDM3 makes the last selected session the default, it seems, without prompting. Once setting the session to "GNOME Classic" you should not have to change it again (of course an update may break this behavior, at which point select "GNOME Classic" again).