I sell an ebook that includes 2 hours of mp3 audio. The file is large and when people purchase it they receive a dowload link to download the zipped file. However some people are not able to open the file, they get the following error message: "Unable to unarchive "file name" into desktop. (Error 1 - Operation not permitted." I researched and downloaded supposedly a good program for creating zipped files that are supposed to be compatible on macs and pc's, but it seems to not be working. Do people know of any good solutions to this problem?