This information applies to version(s): 4, 5, 6
If you have installed Photoshop Elements on your computer, this process runs in the background even if the program is not started.
Please, open Task Manager (press the three keys [Ctrl]+[Alt]+[Del] simultaneously on your keyboard), search for the process "Photoshop Elements File Agent" and close it. Then start the installation of Nik Collection again. After your next reboot, the Photoshop Elements background task will resume automatically.