Re: Access to the specified resource (Not Allowed to access *) has been forbidden.
The API key can be reused against multiple accounts and doesn't need to be generated by the same account that you are attempting to access. The 403 forbidden including a username in the error generally indicates that you have a valid username/password in your authentication credentials (otherwise you would receive a 401 unauthorized) but you are attempting to access a resource you don't have access to. Any chance you could post the code you're using (hiding any sensitive information of course), could be something simple that we could help with.
You can also email our team with the project/files so we can try looking at that by email firstname.lastname@example.org. This is usually the best way to get us code.
Dave Berard Senior Product Manager, Constant Contact