By default, WinDates is not compatible with Windows 7. This means that a compatibility tweak needs to be used. However, if you have received errors with the application, attempt a re-install of the program. This will fix possible corrupted files, registry entries, settings. Try to perform a re-install and then right click the main executable and select Preferences > Compatibility > Windows XP and it should run normally. If you keep having issues, create a new Windows account, log on and install it.
