Symantec Clicktime Protection is no longer scanning the link you have opened. The site you are trying to visit may be harmful. If you know the site is safe, you can proceed by copying the following URL and pasting it into your browser:
http://click.mheducation.com/n0FD03n01P0q0FK0mj02h0p
Learn more about Advanced Threat Protection and how Symantec can help you.