Im at a loss. I have distributed rendering working correctly, but I cannot get these license request errors to go away in rush. Are you rush users out there buying standalone licenses for all your render nodes?
It should work, i think. We use Renderpal and that works. Try to access your licensing web interface and have a look at the available licenses. Dunno exactly how right now, but it should be stated in the licensing and install docs.
Can you render locally on one of your slaves? Is it able to get a license then?
Is this on Mac OS X? If yes, then the error means that V-Ray could not connect to the license server - probably the IP address of the server is not configured properly (using the setvrlservice.exe tool).