This is reproducible on all nodes here with 5.1 RC1. All are running Mono 2.10.6, OS X 10.7.2
Start the client setup wizard on a configured node, as though you plan to adjust a setting. Adjust, if desired, anything other than the repository path - leave that alone.
Click OK to dismiss the wizard.
Now start the slave. It will complain that the repository location has not been defined and ask you to set it. 
If you set it here, the slave won’t prompt in future. You can re-confuse the slave by repeating the above.
Thanks for reporting this! We’ll try to reproduce, and hopefully fix it in the final release.
Cheers,
We can’t reproduce this. I wonder if your global deadline.ini file is corrupted or something, although that would be strange if that was the case on all of your nodes.
Maybe as a test, go to /Applications/Deadline/Resources and rename deadline.ini to deadline.ini.bak. Then run the client setup wizard and set the values. If you run the slave now, it should run as normal. Then close the slave, run the client setup wizard again and close it. Then run the slave again to see if you can reproduce.
Cheers,