As you can see on the official web page, the ActiveThreed Plus software (formerly Sheridan ActiveThreed) is compatible only with Windows XP, Windows ME, Windows 2000, Windows 98, Windows NT 4.0, and Windows 95. Even if you used it on Windows 7 and Windows 8 platforms, you may not have the same luck when you're running the program on Windows 8.1. A solution to solve the problem can be the Compatibility Mode. Right-click the icon of the program, select Properties and then open the Compatibility tab. Check Run this program in compatibility mode for box, select a compatible platform from the drop-down list, press Apply and then OK. After that, right-click again the launcher and select Run as Administrator. If this doesn't help, try contacting the official developers using the Contact Us page.