Error when running Xcode sample projects

I've been through some sample code downloaded from the net and after opening a project and attempting to build it I was greeted with the following error:

"There is no SDK with specified name or path 'Unknown Path'". This is likely because those samples were built with a different version of the SDK than those I had installed.

A simple fix is to go to Project->Edit Project Settings, then go to "Base SDK for All Configurations" drop-down list and pick a version that you have installed on your system instead of the grayed (missing) one that's displayed.