What is causing this error when I try to install the pg gem?

I'm trying to install the pg gem.

bens-macbook-pro:liferecord ben$ bundle config build.pg --with-pg-config=/users/ben/postgresql/bin
bens-macbook-pro:liferecord ben$ bundle install

I get this error:

Installing pg (0.10.1) with native extensions /Users/ben/.rvm/rubies/ruby-1.9.2-p0/lib/ruby/1.9.1/rubygems/installer.rb:483:in `rescue in block in build_extensions': ERROR: Failed to build gem native extension. (Gem::Installer::ExtensionBuildError)

/Users/ben/.rvm/rubies/ruby-1.9.2-p0/bin/ruby extconf.rb --with-pg-config=/users/ben/postgresql/bin
Using config values from /users/ben/postgresql/bin
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
    --with-opt-dir
    --without-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/Users/ben/.rvm/rubies/ruby-1.9.2-p0/bin/ruby
    --with-pg
    --without-pg
    --with-pg-dir
    --without-pg-dir
    --with-pg-include
    --without-pg-include=${pg-dir}/include
    --with-pg-lib
    --without-pg-lib=${pg-dir}/lib
    --with-pg-config
extconf.rb:13:in ``': Permission denied - /users/ben/postgresql/bin --includedir (Errno::EACCES)
    from extconf.rb:13:in `<main>'

What is causing this error?

Extra info:

I installed PostgreSQL from the one click installer.

Here is the output of the directory that I point to for pg-config:

bens-macbook-pro:bin ben$ ls
clusterdb       droplang        pg_archivecleanup   pg_dumpall      pgbench         postmaster
createdb        dropuser        pg_config       pg_resetxlog        pltcl_delmod        psql
createlang      ecpg            pg_controldata      pg_restore      pltcl_listmod       reindexdb
createuser      initdb          pg_ctl          pg_standby      pltcl_loadmod       vacuumdb
dropdb          oid2name        pg_d开发者_开发问答ump         pg_upgrade      postgres        vacuumlo

I'm running:

Rails 3.0.1
Ruby 1.9.2
OSX 10.6.6

In case anyone else has this problem, the error was caused by this:

bundle config build.pg --with-pg-config=/users/ben/postgresql/bin

It should be

bundle config build.pg --with-pg-config=/users/ben/postgresql/bin/pg_config