Why is this popping up in my pc - the application cannot be started. User installation could not be completed.

I cannot open my Libre Office files.

What operating system and release? What version of Libre office? If on linux open terminal and type libreoffice and see if error messages.

This pops up because of what it states and therefore install your application completely (assuming that the application is LibreOffice). If the installation of LibreOffice throws an error - please add additional information by editing your original question.