Switchdesk is the program that allows you to switch your desktop environmnet and it seems that it cant find the image that it displays. There are a few ways you could solve this problem. I do not know where RH9 stores the switchdesk.png image, however I would look at your dmesg and try to find out where it is looking for the switchdesk.png image. On my FC4 box I have the switchdesk.png image located
If you can find where RH9 is looking for switchdesk.png, I would grab a copy of the switchdesk.png image from the switchdesk-gui tarball and move it to the appropriate locations.
Otherwise you can try to uninstall and install the switchdesk-gui using yum.