This nasty bug has been around for over a year: Calling Emacs on Ubuntu from the console outputs
murrine_style_draw_box: assertion height >= -1' failed`
after every action within Emacs.
The solution is simple, but has not been integrated in the Ubuntu repository yet.
Here it is:
In the file
/usr/share/themes/Ambiance/gtk-2.0/gtkrc
change
GtkRange::trough-under-steppers = 0
to
GtkRange::trough-under-steppers = 1
For details see Bug #538541, Bug #550532 and Resolving “murrine_style_draw_box: assertion `height >= -1'"