Thanks Bob for the response. I have not tried yet but i will. As far as i know i will have to run Solaris client version 3.2 on Solaris 2.51 which is not officially compatible with 5.1. But perhaps it can be forced someway - as long as it makes the backups. I dont know when i can attempt this work and i will update this forum after.
I am unable to nfsmount because of the bug in Solaris 8 whereby if the system goes down for whatever reason it causes the other system to hang. I am onsite on Thursday and will try Bob's first suggestion to install a lower version client and if that doesnt work we may blow the dust off the networker configuration.
I can no longer log into my previous account and created a new account with same username. Hence i cant mark this as closed or answered. I no longer have authorization to try to get nbu working on this system. Instead they will rdist the small db running on it and ufsdump the file systems / and /var. Thanks so much to all you who tried to help.