File Not Found error triggering on player.css file in published content

Our web site was scanned recently for broken links, and a handful of our Articulate Studio '13 lessons are triggering a "404 Not Found" error. The two files with url calls that keep coming up are in the player.css file in the mobile directory of the lessons. The two files are "play_100.png" and "ipad_controls_32.png". What's odd is that it appears that all of our Articulate Studio '13 lessons contain references to these files. Yet, I cannot find these files anywhere in the published directories. I'm trying to explain to the person providing me the report why some lessons with this code would trigger a broken link while others would not (and more importantly, why I don't think there's anything I can do about it). I realize that I'm pretty deep in the weeds, but do you have an explanation for why the url calls in the player.css file on lines 997 and 1342 would trigger a file not found error in some instances, but not others? Also, is there anything I can do to prevent the error from happening?