I think I blame this on Microsoft.
I installed the Windows Easy Transfer software on an XP machine to transfer files/settings to a Windows 7 computer. I started up the program and got the code. I got pulled into an impromptu meeting on my way to the new machine. During this meeting I started getting calls from several users about not being able to print.
I soon discovered that only our printers that are attached to external JetDirect print servers are having trouble, which is about a dozen printers. All other printers with internal JetDirect cards were fine. There was a lot of packet loss trying to ping these print servers so I started looking at switches and moving cables around. Didn't make any difference.
After about an hour of messing with stuff I sat down and stopped, because nothing was making sense. Then I remembered what I was doing previous to the meeting and printing trouble. I went back to that XP machine and shut down the Windows Easy Transfer software, just to see what would happen. Packet loss to the print servers was gone and most of the printers started printing again. I had to reboot a few printers, but all is now good.
I use Windows Easy Transfer all the time, but normally starting on a Windows 7 machine. I haven't done it on XP in a long time. Weird.