The multicast IP address %1 is being used by another Windows Deployment Services server, which has IP %2. Use the Windows ...

The multicast IP address %1 is being used by another Windows Deployment Services 
server, which has IP %2. Use the Windows Deployment Services management tools to 
configure your multicast IP address range to avoid this multicast IP address. If 
you allow this overlap to continue, your network usage will be increased.