HP Deskjet 2620 duplex printing option is grayed out

I just purchased an HP Deskjet 2620, hooked up to my desktop running Windows XP.

In the print properties window / layout tab, the "Print on both sides" options are all grayed out.

So, instead, I try to use the "Manual Duplex" check box in the MS Word print dialogue --  it will print the first page, then a pop-up tells me to turn it over and re-insert it in the printer, and press "OK".  Which I do.  But nothing happens.  The window goes away and nothing prints.

Please help!!  I have not had any duplex printing problems with any other printers...

thanks!