Print gives false outside margins message

[Ben]

When I attempt to print a custom size document (3"x7") on
my HP 6310 printer I get the Message "The Margins of
section 1 are set outside the printable area of the page"
but they are not according to the HP manual. When setting
the margins in Page Setup there are no errors detected so
there is no "Fix" button. The document prints normally
with no missing information. This error does not occur
with any standard paper size.