do any of your printers support WSD?
I've got an office with a Lexmark multi function laser that does and it causes some
win7 machines on the network to do this. Check the "ports" section of all network printers on the machine to see if you do. It's odd because they are all identical dells brought at the same time with the same image on them
I still haven't found a real fix for this myself (if this is your problem). However if you do have a WSD printer try turning off wsd support on the printer's control panel and connect to it the old fashioned way (ie standard tcpip port).