Depending on the version of Kontakt you are running, you will need to put the ARC assets in different places. You can download a fresh ZIP of the ARC assets here. Unzip it and place the ARC Folder in the locations below. If there is no “pictures” folder inside the Kontakt folder, then you will have to create one manually by just creating a new folder called “pictures” inside the respective Kontakt folder.
/Documents/Native Instruments/Kontakt 5/pictures/ARC
/Documents/Native Instruments/Kontakt 7/pictures/ARC
So, for example, if you followed the paths above, your folder might look like this for Kontakt 7: