Why is printing broken?
Dia has several ways to print: Dia print, Gnome print and Export as Postscript. A given compilation of Dia uses either Dia print or Gnome print. Dia’s support for Gnome print is currently buggy and disabled by default, but some distributions (Red Hat for one) compile it in anyway. If you have such a version of Dia installed, you can Export as Postscript instead of printing, and then print the resulting file.