So these are local printers then? Are there any setups that don't have this problem? Can you reproduce this on your own machine? It sounds like a hardware problem but not knowing their setup at all makes it kind of hard to guess what it could be.

>The problem exists at a client's site, so I don't know the network structure very well, although I have been to the site. I am getting the errors when I send the files from two computers to two printers (computer A to printer A using report A and computer B to printer B using report B). Reports A and B seem to be identical. I am not sending the files at the same time.