1) If you're creating a new project and you're going to want to change the namespace in the project's Properties, then delete the Form that gets automatically created (Form for a Windows Application project, Class for a class library project, etc). Just delete it. Then go change your project's namespace. Then add a new Form. It will now have the correct namespace. However, I'm not sure what you did that caused errors just by manually changing the namespace. That should have been ok, but you may have missed renaming something somewhere.
I think I missed a rename somewhere. It's compiling fine now.
2) Don't add a new Project from File. Right-click on your Solution in the Solution Explorer and choose Add | New Project.
