make update failing with "a different version ... is already installed"

[Andreas Gustafsson <gson%gson.org@localhost>]

Hi all,

When I try to update a package with "make update", more often than not
it fails, complaining that one of the dependencies of the package has
a different version already installed.  For example, I just tried to
do a "make update" in /usr/pkgsrc/databases/pgadmin3, and got:

  => Full dependency postgresql84-client>=8.4.8: NOT found
  => Verifying package-install for ../../databases/postgresql84-client
  => Bootstrap dependency digest>=20010302: found digest-20080510
  ===> Checking for vulnerabilities in postgresql84-client-8.4.8
  ===> Install binary package of postgresql84-client-8.4.8
  pkg_add: A different version of postgresql84-client-8.4.8 is already 
installed: postgresql84-client-8.4.2nb1
  pkg_add: 1 package addition failed
  *** Error code 1

What am I doing wrong?
-- 
Andreas Gustafsson, gson%gson.org@localhost