I had the same type of problem with Red Hat 7. I got an error when I typed in startx, but it wasn't the same error as yours.
Anyway, Red Hat must use some special commands to configure things. After playing around for a while I just typed in "setup" and it worked. You can actually setup many things by using the setup command, but if you scroll down you will see xconfigurator. That's the one you want.
Oh, and when you are in the setup program the mouse can move, but it doesn't seem to be able to pick anything. You need to use the keyboard only. Look at the bottom of the screen for keyboard instructions. Don't worry, your mouse will work after you exit setup. Just a little tip there. Good luck.