Cannot add Digital Network Port

I must configure 10 Digital printers on new Print Server NT4.0, but everytime I want to add new port, I receive message “Specified port cannot be added. Parameter is incorrect.”. Searching through Microsofts Knowledge Base I found answer that Spooler servise has to be run as System, and be Interactive. But this is case at this server.
It runs as System & Interactive with desktop.
It is SP5 nt4.0 server with up-to-date hotfixes. Spool folder is on separate logical drive. I?ll try to re-set it as default again. But I need to install those printers as soon as possible…
Can someone help?