VS 2008 Add In, Acessing a specific Project Configuration item

Hello All,

I've been working on an addin that modifies certain project configuration items of all the projects in the currently loaded solution.

My method consisted of the following :

Project prj;
Configuration config;
Properties configProps;
Property prop;
string intermediate, output, preprocessor;
if (_applicationObject.Solution.Projects.Count > 0)
{
   int project_count = _applicationObject.Solution.Projects.Count;
   for (int i = 1; i <= project_count-1; i++)
   {
      prj = _applicationObject.Solution.Projects.Item(i);
      config = prj.ConfigurationManager.ActiveConfiguration;
      configProps = config.Properties;
      prop = configProps.Item("OutputDirectory");
      prop = configProps.Item("PreprocessorDefinitions");
   }
}

Except, the call to retrive the "PreprocessorDefintions" property throws an exception. What I'm trying to do is get the value of the Configuration Properties->C\C++->Preprocessor:Preprocessor Definitions.

Can anyone see what I'm doing incorrectly?

Thanks.