Generally this is as a result of another exam software being installed your laptop. Try uninstalling it, prior to using Exam4.
In rare cases it is caused by your account not having full administrative rights to the laptop. Often this is as a result of the laptop provided by an employer. Try using a personal laptop with full rights or get your account on your work machine upgraded to administrator. If you are certain you have full administrative rights, try to uninstall Exam4, then redownload and reinstall.
It has also been found that in some cases the use of third-party antivirus software can cause this to happen. Try uninstalling your third-party security software and replacing it with Microsoft Security Essentials or some other brand of antivirus software.