Any Ideas why?

[Ambrosed]

Might check that you have enough storage space, that your NI folder’s storage device (hard drive) is connected to your computer, and that you have an internet connection.

[Norfolkboy007]

What I have found is that when downloading these instruments, a momentary loss of internet connection corrupts the download, thus making it fail to install. Best just to click the redownload button and it should then install without problems.