ok try this,
when you are in IE, go to Tools -> internet Options -> security
now choose restricted sites and look if you can find Runescape in it
if not just add it to the trusted sites
write this:
http://www.runescape.com
and press add
also reduce the security level to medium
and untick "enable protected mode..."
now go to "General" tab, under browsing history, press delete, to remove all cookies, temp internet folders and history...
after that restart your browser and try again