Comment 4 for bug 133990

I have a similiar problem in gutsy:

(muine:14483): Gtk-CRITICAL **: gtk_widget_grab_default: assertion `GTK_WIDGET_CAN_DEFAULT (widget)' failed

Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object
  at Muine.PlaylistWindow.SongChanged (Boolean restart, Boolean fire_signal) [0x00000]
  at Muine.PlaylistWindow.SongChanged (Boolean restart) [0x00000]
  at Muine.PlaylistWindow.OnPlaylistPlayingChanged (IntPtr playing) [0x00000]
  at (wrapper delegate-invoke) System.MulticastDelegate:invoke_void_intptr (intptr)
  at Muine.HandleModel.set_Playing (IntPtr value) [0x00000]
  at Muine.PlaylistWindow.PlayAndSelect (IntPtr ptr) [0x00000]
  at Muine.PlaylistWindow.RestorePlaylistForeachFunc (Muine.Song song, Boolean playing, System.Object user_data) [0x00000]
  at (wrapper delegate-invoke) System.MulticastDelegate:invoke_void_Song_bool_object (Muine.Song,bool,object)
  at Muine.PlaylistWindow.OpenPlaylistInternal (System.String fn, Muine.PlaylistForeachFunc func, System.Object user_data) [0x00000]
  at Muine.PlaylistWindow.RestorePlaylist () [0x00000]
  at Muine.Global.Main (System.String[] args) [0x00000]