For example:

that message indicates that another process is running and has those files open, preventing the installer from writing them.

This is how to solve those kinds of errors:

-restart your computer
-in the services window (in control panel), make sure the Dragonfly service is stopped (the name may vary slightly)

-In Task Manager, make sure you don't see pythondo.exe running, if you do then kill it via right-clicking on it

You can then install Dragonfly and it should work.