Why can't I download itunes?

it says that apple aplication support is required and to uninstal and try again.. ive uninstalled and reinstalled about 5 times and i just keep getting the same message.. it also says while in the middle of downloding that theres an error with a part of the download. then a little later a message pops up saying that the mobile support device cant download and it gives thee options to abort retry or ignore.. i dont know what to do im getting frustrated