There is no need to kill and redownload the file. All you need to do is to add the file to the iTunes Library. iTunes will play a file no matter whether it is labelled iTunes or Quicktime. If this has not proved true for some of your downloads there is another quite different possible reason. Many record companies, dismayed by the volume of illegal copying, have been seeding the internet with spoof copies that either will not play at all or only play nonsense or abusive messages. Sorry, I should know this could not apply to you because you never do anything illegal, do you?!