Digital BW, The Print

I seem to have a problem with QTRGui 2.2.0.  I'm sending an image to
QTRGui which is 27.7cm x 40cm, to print on A3 paper (which is 29.7cm x
42 cm) at 720ppi.  QTRGui tells me that the image won't fit.  If I
switch between centered placement and specifying the margins manually,
I get a variety of errors, including floating point.

If I send the image at 360ppi, everything works fine.

F_P