I think I may have to use a full media server license??

server-V = virtual
server-A = physical
server-B = physical

I have installed a SAN media server license on server-V to backup the common 
drives and this works fine.
However, when I try to backup the local drives on each individual physical 
server, I get a license use has been exceeded (code 159)


Must I backup the C:\ and D:\ drives on the physical server-A and server-B as a 
regular client over the network to another media server?
or..upgrade to a full media server license?