I finally discovered what was causing this. A custom splash screen that I had installed years ago... I didn't even knew anymore that it was a custom splash screen :)
The strange thing is that gnome-session displays that image but than freezes. And the old gnome-session version works fine with this image. Maybe the file is corrupt though it displays fine in nautilus and eog. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]