problem upgrading gtk2

When I try to upgrade gtk2 I get the following error: /bin/sh: line 1: gtkdoc-rebase: command not found and I am unable to upgrade the package. This happens whether I use "sudo port upgrade gtk2" or "sudo port -f upgrade gtk2". "port outdated" says that I have 2.12.1_0 installed and 2.12.3_0 is the latest version. I don't know what gtkdoc-rebase is. is it part of the gtk-doc package? That package is not installed on my system. cheers Mike