Duplex printing problems on some documents with Word 2003

[Sue]

I have two Word documents. I try to print each of them on the same printer
as duplex. One will print duplex without a problem, the other ignores the
duplex instruction (given via file - print - properties). There are
differences in other print setup between the two documents, but I cannot see
how that would affect the duplexing. Does anyone have any ideas??

Regards

Sue