This error may be caused by the internet connection being down. It can also occur if a internet security software or firewall is blocking the software access to the internet. You will need to check the internet connection and check any security software.
You may also need to reset the internet settings for Internet Explorer : reset Internet Explorer
If you have Windows XP running on your system, then please make sure that it has been updated to Service Pack 3.
Finally make sure that the time and date is set correctly, this can cause some problems.