I didn't find anything about the software regarding the compatibility with Windows 10. I have used all the search engines and find that the Day-Timer Organizer is a discontinued application. This means it won't receive a new version or patch to increase compatibility with Windows 10. You can try applying a compatibility tweak, but that's it.
Right click the installation package, and go to Properties > Compatibility. Choose another operating system from the drop down menu and then launch the application.
