Are you using IOS or VxWorks?
In VxWorks, you need to do the followings to enable multicast:
1. click on "Setup"
2. "Advanced" in the row for radio interface.
3. You can configure the "Maximum Multicast Packets/Second"
You do not need any configuration in IOS, but you need to run 12.2(15)XR2 or 12.3(2)JA because of bug CSCee78082.