DarwinPorts is an easy way to install unix software on your Mac. Here are some tricks and hints about using it.

The Following Version of... are already installed

$ sudo port uninstall gnupg
  The following versons of gnupg are currently installed:
    gnupg 1.4.1_1 (active)
    gnupg 1.4.2_0
Error: Please specify the full version...

How you fix this issue is to use the @ paramter in the page. Observe:

sudo port uninstall gnupg @1.4.1_1

The @ lets you specify the version.