I had this problem too-- apparently caused by the USPS "Click 'n' Ship" program which exercises an unusual amount of control over the pdf output-- until the last version it was print only, no copies, no saving, no nothing. New version of "CNS" made pdf file saving possible (up till midnight on the day you do it, some how) but also managed to check the print-to-file- box I've unchecked it and we'll see if it sticks later this afternoon.
It took me so long to find this thread, note the problem, and fix it, because I found a relatively simple workaround! When the print routine asks for the output filename, I typed in "LPT1:" I was warned that the filename was already in use, did I want to overwrite it? I said yes, the error message disappeared, and the document went through to the selected printer. This is odd to begin with because I have no idea what wierd brain-static made me try that, but it gets worse. The selected printer is a USB printer, on a USP "virtual port." LPT1: goes to a thermal printer used only by the UPS shipping program.
A decades old habit would have me not look a gift horse in the mouth-- it's often (almost always in fact) eaiser to standardize the workaround and not waste time worrying about the oroginal problem. But this required a few extra keystrokes every time I went to print a USPS label, so I found this forum and thread easily with Google and the problem is solved.