Browsers can't open specific site but works fine in another account?

I have a job that requires me to log in to a webpage. In my current Windows user account, no matter what browser I use, I always get a 500 Servlet Exception error. I tried updating Java and disabling my firewall but I still get the error. Then I created another user account and am able to log in to that page using Firefox and IE. So it shouldn't be because of the browsers or security programs. Maybe I messed up some windows settings? Does anyone have any idea on what could be causing the problem and what I can do to fix it? I can't afford to reinstall windows. Thanks!
btw, I'm using Windows 7 home premium 64 bit.

Any ideas? Really need some help here...

If you're not using the 32-bit version of IE, you could try that instead.

Had similar problem but different error. I completely uninstalled IE8 and re-installed. That worked for me. Unfortunately a few weeks later the problem showed up again in IE8. Finally I dumped it and just kept FF. No more problems since. Did not have to re-install Windows.

Also before you do this; did you try to "Reset" IE8 or try to access the trouble site running Firefox in safe mode?

A Guy said:

Have you changed your host file? Perhaps added that site somehow? A Guy

But the host file is the same for all users of a computer as it is inside the windows system files and not in the user's account. If he can open with a new user account then it is surely not hosts file problem. I feel it might be a malware/spyware problem.

I would advise to run a full security check including anti-virus, anti-malware and anti-spyware to make sure it is not due to it.