First understand the main features of the following DLL file. DLL file (dynamic Linkable library, which is dynamically linked libraries file), is a file that cannot be run separately, allowing programs to share the code and other resources necessary to perform special tasks. So when you have the system file DLL changes, it will cause DNF can not open, run the wrong situation.
Solution: The first is to prompt you to reboot to solve the problem, the user first try to restart your computer to see if you can repair the fault. After that, if you can't fix it, check to see which DLL is being altered or lost, and you can download the DLL file directly on the Web and copy the file to the C:windowssystem32 directory. If the failure is still unresolved, uninstall your DNF application and start it again on the disk, which will definitely fix the system DLL changes.
Believe that through the above methods you can know DNF found that the system DLL has changed how to solve it.