I'm not able to boot fedora 15 in runlevel 5. After all services start, when the login screen should appear, gdm just show a mouse waiting cursor and keeps restarting itself.

From /var/log/gdm/\:0-greeter.log

Gtk-Message: Failed to load module "pk-gtk-module"
/usr/bin/gnome-session: symbol lookup error: /usr/lib/gtk-3.0/modules/libatk-bridge.so: undefined symbol: atk_plug_get_type
/usr/libexec/gnome-setting-daemon: symbol lookup error: /usr/lib/gtk-3.0modules/libatk-bridge.so: undefined symbol: atk_plug_get_type

Where should atk_plug_get_type be defined?

Edit: Here a better description of the error

(system-config-network-gui:2643): Gnome-WARNING **: Accessibility: failed to find module 'libgail-gnome' which is needed to make this application accessible
/usr/bin/python: symbol lookup error: /usr/lib/gtk-2.0/modules/libatk-bridge.so: undefined symbol: atk_plug_get_type

Why there are still references to gtk2? Did preupgrade fail? Attaching upgrade log... it seems gdm was not added, but it is present in the users and groups list.

May 26 11:25:52 sysimage sendmail[1076]: alias database /etc/aliases rebuilt by root
May 26 11:25:52 sysimage sendmail[1076]: /etc/aliases: 77 aliases, longest 23 bytes, 795 bytes total
May 26 11:46:09 sysimage useradd[1793]: failed adding user 'dbus', data deleted
May 26 11:53:37 sysimage systemd-machine-id-setup[2443]: Initializing machine ID from D-Bus machine ID.
May 26 11:55:28 sysimage useradd[2835]: failed adding user 'apache', data deleted
May 26 11:55:38 sysimage useradd[2842]: failed adding user 'haldaemon', data deleted
May 26 11:55:43 sysimage useradd[2848]: failed adding user 'smolt', data deleted
May 26 11:57:32 sysimage sendmail[3032]: alias database /etc/aliases rebuilt by root
May 26 11:57:32 sysimage sendmail[3032]: /etc/aliases: 77 aliases, longest 23 bytes, 795 bytes total
May 26 11:57:46 sysimage groupadd[3066]: group added to /etc/group: name=cgred, GID=482
May 26 11:57:47 sysimage groupadd[3066]: group added to /etc/gshadow: name=cgred
May 26 11:57:47 sysimage groupadd[3066]: new group: name=cgred, GID=482
May 26 11:58:42 sysimage useradd[3086]: failed adding user 'ntp', data deleted
May 26 12:00:13 sysimage dbus: avc:  received policyload notice (seqno=2)
May 26 12:15:08 sysimage useradd[4950]: failed adding user 'gdm', data deleted
May 26 12:24:39 sysimage dbus: avc:  received policyload notice (seqno=3)
May 26 12:25:24 sysimage useradd[5522]: failed adding user 'mysql', data deleted
May 26 12:25:37 sysimage useradd[5533]: failed adding user 'rpcuser', data deleted
May 26 12:26:31 sysimage useradd[5592]: failed adding user 'tcpdump', data deleted

Any suggestions before I revert installation to F14?