To access the lab content on, make sure that you allow third-party cookies from the following domain: in your browser. Another option is to select "allow all cookies" and that will also work. The cookies are required to keep track of your lab sessions, progress, and state within the lab client. 

The following links will help you configure the above for each browser:
After this you should stop seeing the Access Denied error. If you need further help, please reply to this e-mail so we can assist you further.