Please let us know the system date displayed on your computer.
Are you able to change the system date through "date and time" settings in Control panel.
If your system date is wrong this issue may happen. To work around this behavior of "revocation error message", manually configure your proxy server settings:
Start Internet Explorer.
On the Tools menu, click Internet Options, and then click the Connections tab.
Click the appropriate connection, and then click Settings.
Under Automatic configuration, click to clear the Automatically detect settings check box.
Under Proxy server, click to select the Use a proxy server for this connection check box.
Type the address and port number of the proxy server that you want to use in the Address and Port boxes.
If do not want to use the proxy server for local (intranet) addresses, click to select the Bypass proxy server for local addresses check box.
Also, check in your Event viewer (Start>Run>Control Panel>Administrative Tools>Event viewer>System) to see if you have a lot of W32Time errors. You may have the wrong synchronization server listed in the Date/Time settings, or XP may not be synchronizing properly to Time.Windows.com. I used a separate time synch utility called Dimension 4 to solve the problem with my XP.
I have had this problem as well recently, as the time can be out by 5-10mins,I changed it to time.nist.gov and it seems to be ok now.However if the problem does come back the Cmos battery is the next step.