Can't update ports with portupgrade

==>  Installing for pkgconf-0.8.9
===>   Generating temporary packing list
===>  Checking if devel/pkgconf already installed
===>   An older version of devel/pkgconf is already installed (pkg-config-0.25_1)
      You may wish to ``make deinstall'' and install this port again
      by ``make reinstall'' to upgrade it properly.
      If you really wish to overwrite the old port of devel/pkgconf
      without deleting it first, set the variable "FORCE_PKG_REGISTER"
      in your environment or the "make install" command line.
*** Error code 1

Stop in /usr/ports/devel/pkgconf.
*** Error code 1

Stop in /usr/ports/math/fftw3.
*** Error code 1

Stop in /usr/ports/math/fftw3.
** Command failed [exit code 1]: /usr/bin/script -qa /tmp/portupgrade20130127-17768-w2kh2d env UPGRADE_TOOL=portupgrade UPGRADE_PORT=fftw3-3.3.1 UPGRADE_PORT_VER=3.3.1 make
** Fix the problem and try again.

...

--->  Packages processed: 47 done, 0 ignored, 70 skipped and 9 failed