Error 403?

Greetings

I have just tried adding wp to a subdomain for the first time.
(/introduction.4yoursuccessnow.com)
I get the following..
Error 403 – Forbidden
You tried to access a document for which you don’t have privileges.

4yoursuccessnow.com/wordpress is already installed – so I am wondering is there is a conflict and how to overcome this.

Any thoughts?
htaccess file maybe?

Thanks

Graeme