WPrefs crashes with segmentation fault

Hi,
somehow my WPrefs application has stopped working in FreeBSD 5.4. I have 
Window Maker 0.91.0 installed.

I was installing the Thunderbird email port from XWindows, and I started 
the WPrefs app to add a new item to my Applications menu. Thunderbird 
finished installing and I saved and closed WPrefs. From then on when I
try to run WPrefs it crashes. If I run the command:
/usr/X11R6/GNUstep/Apps/WPrefs.app/WPrefs
from a terminal I get a 'Segmentation fault (core dumped)' error.

I thought I might be able to fix this by pkg_deleting WindowMaker and
reinstalling it, but this hasn't worked. I've also tried moving aside
the /usr/ports/X11-wm/windowmaker directory and getting it again with
cvsup, but the crash still occurs.

Is there anywhere I can look for log files so that I can get a better
idea of what the problem is? Can anyone think of how to fix this? I'm 
new to freeBSD and am still struggling to find my way around.

Thanks.
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