I have a Mac Mini with Mountain Lion and a Windows 7 PC. I was able to download seven YouTube videos (one .avi and the rest .mp4) on my PC and copy them into a folder named "Science". I then transferred the folder to a to a USB flash-drive that plays OK on my PC.
However, when I drag-and-drop that folder from the USB flash-drive to the "Movie" folder of my Mac Mini hard drive, I do not see the folder listed in the "Finder". Also, If I try to drag the folder again to the Mac Mini, I get the message that it already exists on my Mac Mini (even though I can not see it in Finder). So I drag it again and still can not see the folder. Why am I having this problem?