Using Google.GData in C# to update POP3 settings

I'm creating a desktop app using C#. I've downloaded the Google.GData.Application to start working with the API. From this link I found this code:

            var service = new GoogleMailSettingsService("my domain", "API KEY");
            service.setUserCredentials("my username", "my pass");

            var res = service.UpdatePop("my username", "true", "ALL_MAIL", "KEEP");

I created a simple console app and ran this code (it is the only code running). However whenever I run it, I get an exception with the 403 status code. My question is:

1. Is there anything wrong I've done? I mean, is there any additional step(s) I need to take? I've got the my domain and API key parts from here. I registered a domain and added the code and information to get the codes.

2. Is there any way to not use my domain? This app is not for me and is not a web app that is on a specific domain. It's a desktop app and is expected to run on any machine with .Net installed.

Thanks.

Make sure the user you are authenticating with is an administrator for the Google Apps domain.

The API Key is not required when using ClientLogin (i.e. authentication with username/password), the second parameter for the GoogleMailSettingsService constructor is just a string identifying your application.