This error occurs in older versions of Google Desktop and has been resolved with the newer versions. For detailed information about the latest Google Desktop release number, please visit http://desktop.google.com/support/bin/answer.py?answer=34180
To find out which version of Google Desktop you're currently running, visit your Google Desktop homepage and click the "About" link at the bottom of the page. On the bottom of the About page, you should see your version number, "Google Desktop 5.x.xxxx.xxxxx."
3. If you want to add new material without losing your previous index, make sure the box next to "Keep my index" is checked. If you want to entirely replace your previous index, un-check the box.