Gnome 3 "Oh no!" error on login

Question

On Fedora 17, after instaling the Java runtime and (L)AMP (I do not think it is even related, I didn't restart for quite a while) and restart and login the "Oh no! Something went wrong." message appears. This error message is utterly useless (I'd even say, "Windows-like"!). I've done some investigation, but do not know how to fix these errors nor do I know whether they're even related:

cat /var/log/gdm/:0-greeter.log

Window manager warning: CurrentTime used to choose focus window; focus window may not be correct.
Window manager warning: Got a request to focus the no_focus_window with a timestamp of 0.  This shouldn't happen!

(gnome-settings-daemon:1387): GLib-GObject-CRITICAL **: g_object_unref: assertion `G_IS_OBJECT (object)' failed

(gnome-settings-daemon:1387): GLib-GObject-CRITICAL **: g_object_unref: assertion `G_IS_OBJECT (object)' failed
g_dbus_connection_real_closed: Remote peer vanished with error: Underlying GIOStream returned 0 bytes on an async read (g-io-error-quark, 0). Exiting.

(After doing some... well... stuff (including an attempt - not sure, if succesfull - to disable the extensions, they don't load anyway), the last row changed and I'm ashamed to say I forgot the original error. This is the current one.)

lspci | grep -i vga

00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
01:00.0 VGA compatible controller: nVidia Corporation Device 124d (rev a1)

(I have Intel HD / nVidia cards and I use Intel HD one, using the default driver. No Bumblebee or stuff like that and things worked this way all the time.)

KDE works fine.

Any ideas either for the fix or for some further research? Thanks in advance!