I once had such a problem when I updated xfree86. Cause the problem is also in xfce it's probably a xfree86 problem (I 'm running gnome). I solved it by reconfiguring my x-server:
- First make a backup of the file /etc/X11/XF86Config-4. Reconfiguring your x-server could fail, and it's always nice to have a way to go back.
- Execute /usr/X11R6/bin/xf86config. After you have gone through this program, save your configuration to /etc/X11/XF86Config-4. The previous config-file may give you some hints.
Hope this will help. You can always go back to your old configuration by putting your old XF86Config-4 back, in case you totally mess things up
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Succes!
Corien