I have the same problem but I´m able to backup from the client, but when I try to make backup from the backup server, I get the "Conection refused error".
I´ve 12 Netware clients, and none of them answers to rpcinfo, but I´m able to ping all of them. Only one client doesn´t backup, the others goes fine.
Client features:
Netware 4.11 SFT III , con el Support Pack 6.
Version TSA. TSA410.NLM version 4.16, 24-Jun-99.
Version de Networker: 4.21
And the most strange when this machine is rebooted is that the scheduled backups of this client goes fine during three or four days.