I've had this issue with several systems at a site I upgraded to Windows 7 a couple months ago. Some or all of a systems network printers would stop working. Looking closer I found the printer ports and driver list would be empty. Local printers were still working and other users were still able to print to the network printers. I found that restarting the local system's print spooler would resolve the issue for a while. Their print server is still running Server 2003. But I just found this post on another forum and thought I might save someone else some grief.

http://www.sevenforums.com/crashes-debugging/39769-printer-ports-disappearing-network-win7-machines.html

Matt

Legacy Forum Name: Missing printer ports,
Legacy Posted By Username: connectex