You have this problem, because the installation process is not completed or some files are missing. In order to fix it, you need to reinstall the software.
If you use Windows XP or below you can go to Start > Control Panel > Add or Remove Programs. In the Currently installed programs box, click on the WinDVD program and then click Remove.
If you have Windows Vista or above you need to go to Start > Control Panel > Programs > Programs and Features. Select the WinDVD application and click on Uninstall.
After that, download a new copy of the program and install it using the serial key received when you purchased it.
Also, if the software is completed installed and works well, but the error still appears, go to Start, type msconfig and open the utility. Select the Startup tab and un-check the box next to WinDVD. Click Apply and then OK.