My first thought on this is to check your share on your jumpstart server, it should be shared as ro. This should be done automatically by the add_install_client.sh so it should be ok.
Next what are the permissions on your boot image directory? /export/jumpstart/Solaris_2.8/Tools/Boot I presume it was a standard install to the jumpstart server so this again should be ok.
Is the IP/netmask of the machine you are trying to jump on the same subnet as the jumpstart server?
What does the /etc/bootparams on the jumsptart server say? Is it correct in pointing to the correct locations?
Looking at your error again, why is it requesting the ethernet address of your jumpstart server? ...and is it resolving? You should be on the same subnet or have additional nic's on the jumpstart server for each subnet you are jumping, or use a boot server on each additional subnet to boot your host onto the network and then access the jumpstart server.