Multicasting "network is unreachable"

I am trying to get Multicast imaging running in our environment. (Zenworks 11.2.1, and ENGL Imaging Toolkit)
Because our switch does not support multicast routing i have created a sattelite machine with the imaging role in the same subnet as the clients.

When i want to start the multicast session manual (img -session test - master) then i got the error message:

Multicast session: test (master)
Elapsed time:00:00
Network is unreachable. Unable to connect to server.


I get this message at the master but also at a client machine.

I can ping the Sattelite server (same subnet).

Does anyone have an idee where to start troubleshooting?

Regards,
Sander