1) There is an error stating to close all the running Movavi applications. 

Please make sure that you do not have any other Movavi applications running. 

Note that depending on your settings, they might also run on the background, e.g. a watchfolder in Movavi Video Converter, or screen recorder might be in the waiting mode, so you might want to check your Processes tab in the Task Manager (press Ctrl + Shift + Esc or Ctrl + Alt + Del keyboard shortcuts) and end the unwanted processes. 

You might also want to reboot your PC. 

2) You cannot find an installation file to launch.

It might be the case that the download has not finished yet.  

Press Ctrl+J  keyboard shortcuts to check that. 

You can also check your Downloads folder and find the downloads made today.

Else, use a different web browser for a download.

Try using your license information, or use our Downloads list.

3) The error message states that the installation file is damaged. 

Please try turning off your Firewall and Antiviral program for a moment. Then, download the installation file once again.

You can find installation files of all programs here.

4) If you have a NSIS error, please check the suggestions provided per this instruction.

5) The installation is running without any visible problems, and then the error states that some DLL is missing.

This kind of errors can be resolved by reinstalling the application and temporarily disabling the antivirus software.  

6) The installation was successful, but the application does not start.

Please review this article