Can't login from dashboard

I'm working on a site for a client that was setup by someone else using their WPMU-DEV account. The client now has there own WPMU-DEV account (which I can log in to on your website). I have logged out of the dashboard in the site but when I try to login with the clients new details it errors. I notice it is still sending the OLD account details in the URL on your site.
Also the site is not linking to the clients 'hub'. How can I clear any details of the OLD account?