I am running OS X 10.9.5 (13F34) and whenever I try updating to Yosemite I get the error message which says "OS X Yosemite failed to download. Use the Purchases page to try again". I tried installing the Yosemite Beta 4 and it refused to install giving the same error message. My computer which is a mid 2013 MacBook Air has 20.4GB free space. All other third party applications and system updates can be updated without problme but when I try updating to the new operating system it gives an error message. As a last resort I connected using the Unotelly servers thinking maybe the problem has to do with limitations on my college WiFi but still keep getting the same error message.