We have a few invoices that have tables in them and when we print them 1 or more lines (but not all) will come out thicker than the others.  When you look at it on the screen before you print the lines look equally thin so I'm not sure what's going on.  We've tried to print using postscript but that doesn't seem to help.

that is what I thought too but we've tried printing on different printers and it happens on all of them.