|It depends what application you were using when the error popped up.|
If it happened while using a web-browser, and that browser is the default IE6, IE6 is very much out of date now. However, as there is no newer version of IE for Win2K, and continuing to use Win2K is no longer supported by Microsoft and poses a significant security risk, you are strongly encouraged to upgrade your Windows version to one that is still supported and which can be kept up-to-date.
If that is not possible, you'll need to use an alternative web browser. The last version of Firefox compatible with Win2K was version 12 here: http://www.oldapps.com/firefox.php?...
However, that too is an old version that cannot be updated on Win2K.
The other alternative is Opera but I can't verify it being compatible with Win2K: http://www.opera.com/browser/download/
As you can see, you are hampered by an out of date operating system.