First, I could successfully download and install IOS 9 Beta on my iPhone 5 (Model A1429). It works fine.
Second, I also could successfully download and install Mac OS 10.11 on my iMac Mid 2009. It also works fine.
Third and here my trouble starts:
Then I tried to download IOS 9 Beta for my iPad Air (Model A1474). The download starts, but
after two, three seconds instead of the download file I get a text file named "unauthorized" with the following content:
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How can I negotiate the loop of unsuccessfulness?