Ubuntu-tweak a fatal erroc occured

[DeAverk]

Traceback (most recent call last):
  File "/usr/bin/ubuntu-tweak", line 76, in <module>
    launcher = TweakLauncher()
  File "/usr/bin/ubuntu-tweak", line 43, in __init__
    window = MainWindow()
  File "/usr/lib/pymodules/python2.7/ubuntutweak/mainwindow.py", line 180, in __init__
    self.update_model()
  File "/usr/lib/pymodules/python2.7/ubuntutweak/mainwindow.py", line 280, in update_model
    self.LOGO_COLUMN, MLOADER.get_pixbuf(module.__name__),
  File "/usr/lib/pymodules/python2.7/ubuntutweak/modules/__init__.py", line 75, in get_pixbuf
    pixbuf = icon.get_from_name(module.__icon__, size=24)
  File "/usr/lib/pymodules/python2.7/ubuntutweak/utils/icon.py", line 27, in get_from_name
    pixbuf = icontheme.load_icon(alter, size, 0)
GError: Icon 'gtk-execute' not present in theme