some downloads are successfully played and some are not even when downloading is complete. Launch button does not launch music. Double-clicking in the shared file does not play music either. Later these non-functioning files even disappear while working files continue to work. any idea?

some of the downloads seem to be of a Microsoft variety that seems to be unrecognized by the Mac. I have the icons of Macast, Audion, SoundJam and Quicktime on my desktop. Usually the Macast will open the blank looking file formats, and create a Macast file. Then you can plunk it down in any of the others like Audion and it will then play. Try to drag the file onto the icon of the player, not just click on it..this seems to work better.(for me anyway)