The media check built into the YDL 5.0 installer does not function. Instead, you may conduct a media check as follows. From the command line: md5sum /[path]/[to]/[ydl].iso [ENTER] ... which will output an MD5SUM which you compare against the MD5SUM in the MD5SUM file. To check your media from Windows, select one of the tools mentioned here: http://www.linuxquestions.org/linux/answers/LQ_ISO/Checking_the_md5sum_in_Windows To check your media from OSX, follow the instructions posted here: http://lists.terrasoftsolutions.com/pipermail/yellowdog-newbie/Week-of-Mon-20040510/005632.html For YDL 6.0, use the built in Media Check function of the installer.