Unknown system error printing to NT

Hello;

We are suddenly having a problem where all of our printer queues keep giving us an unknown system error and asks us to reboot. Sometimes we will be able to print after that and sometimes it won’t work at all. I thought the problem was available disk space, but I made some changes over the weekend and freed up a bunch of space. They are connected through TCP/IP and I’m able to ping them. If I go through the server’s control panel, it says they are on-line and ready to print. Any thoughts?