I got this to work. When the error is received, change genclntsh as it says above, that is:
Then the trick is to run the script.
It takes a couple minutes to run and you may get a warning (I did). Finally, it will give a message about a file being created. Click retry in the installer.
Also, make sure you have the a new version of open-motif installed, or you will get a lot more errors. I installed the version on my Red Hat install discs.