Are these errors in .xsession-errors important?

[Chris G]

I'm getting the following error 38 times in .xsesion-errors when I
start up xfce (on xubuntu 9.10):-

    ** (xfwm4:17549): CRITICAL **: getBoolValue: assertion `G_VALUE_TYPE(rc[i].value) == G_TYPE_BOOLEAN' failed

Is this anything to worry about?  Can I fix it?

-- 
Chris Green