Hmm, we don't see that here on our Vista Ultimate machine, upgrading from 1.8.978, but one thing you can try is:
1) Go to the control panel and uninstall the current version. Pay special attention during the uninstall -- it will ask you if you want to KEEP the existing data. Be sure to keep the existing data.
2) Download the setup from www.bigoven.com/downloads/bigoven1.exe and install it.