Its trying to use xmessage to give you a message. basically, xmessage needs to exist to see the messagee
no matter, you can trace the message it tries to send.
Try doing this:
and use a text editor to find line 169 of fbsetbg. the whereis should say where it is. Use an editor with a line number indicator
Also its useful to be root while your at it... if whereis wont find it, try
find / -name fbsetbg
Then post what the line says. If the message lasts longer than a line, post it all. Also, read it
it should be error or message that can explain wtf is up.