I had the same problem and had to go into the security settings and make play.net a trusted site. I think its because IE 10 runs everything in protected mode and it doesn't like something that play.net is using.
Tools, Internet Options, Security, click on the Trusted Sites green check mark, then click on the now active Sites button below it, click off the Require server verification (https) for secure sites, then either type in play.net or you can just hit the add button if you're there already (I was able to use google to search for play.net/gs4 and click on it to get to the gs4 front page, but nothing else would work including my favorites).
Hope that helps, I assumed it would be easier than trying to get Simutronics to fix whatever the problem is with their website. Hopefully they aren't stealing my credit cards and buying porn with them. :)
