Can you try going to Windows Control Panel -> Add/Remove Programs, and uninstalling BigOven (when prompted, choose NOT to delete your exisitng recipe boxes/shopping lists).
Then, re-download from http://www.bigoven.com/downloads/bigoven1.exe, saving that file to your PC (anywhere will do). To install, double-click on that saved bigoven1.exe file. If you still get an error message, please let us know specifically what it says... thanks!