Symptoms
The AddConfiguration automation method fails with the following error when called from a Developer Studio macro and the active project is a makefile project:

The configuration could not be added to the project.
Resolution
Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.
This bug was corrected in Visual Studio 6.0 Service Pack 3. For more information about Visual Studio service packs, please see the following articles in the Microsoft Knowledge Base:
194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why?(http://support.microsoft.com/kb/194022/EN-US/)
194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed?(http://support.microsoft.com/kb/194295/EN-US/)