Printing mailing labels from Contacts. Why only single address printed, not complete set

I am trying to print mailing labels from a group within my Contacts addresses. In the Print dialogue I can see the first page of 21 addresses laid out correctly, but only a single address is printed. I have selected all of the addresses within my "Xmas address" group and am using an Avery template from the print dialogue window. What am I doing wrong in what seems to be a very simple process?