cannot set background in icewm

[Andras Lorincz <andras.lorincz@gmail.com>]

I'm trying to set a background image in icewm with icepref but when I
press the reload button I can see this error in the console from where
I started icepref:

Traceback (most recent call last):
  File "/usr/lib/python2.3/site-packages/gtk-1.2/gtk.py", line 111, in __call__
    ret = apply(self.func, a)
  File "/usr/bin/icepref", line 1934, in set_file_settings
    self.update_widgets()
  File "/usr/bin/icepref", line 1798, in update_widgets
    self.widget_dict[widget].set_value(self.settings[widget][VALUE])
KeyError: 'KeySysWorkspace11'

Could someone give me some hints what this means?