I have Norton Internet Security installed

This causes problems with the functionality of many complicated web applications such as the Narrowstep Player.

You will need to allow pop-ups and JavaScript from http://player.narrowstep.tv.

Also, try this page on the Symantec site:

http://service1.symantec.com/SUPPORT/nip.nsf/docid/2004093010421136?OpenDocument&src=hot&prod=Norton%20Internet%20Security&ver=2006&csm=no&seg=hho&tpre= 

or try searching Symantec for more info:  

http://www.symantec.com/techsupp/home_homeoffice/products/nis/