Error message: "Please quit your Internet browser before continuing"

I puchased Norton AntiVirus 12 for Mac® (For OS X 10.7 Lion) . 

 

I'm attempting to install the application, but I keep getting the message to "Please quit your Internet browser before continuing" with the explanation that Safari is open and needs to be closed.

 

My Safari browser is closed. In fact, I've restarted my Mac and have attempted to install the Norton antivirus application immediately after I log onto my Mac, but I still get the message that I need to quit my browser.

 

What's up with this?