SCCM 1511 HOW TO FIX DOWNLOAD PACKAGE ISSUE IN THE CLIENT SIDE
The main error that you got after upgrading clients from SCCM 2012R2 to SCCM 1511 is "main error "!
If you check CAS and DataTransferService log, you will find "Download failed for download request " and"Error sending DAV request. HTTP code 401, status ‘Unauthorized’".
This error is related to IIS. Checked the IIS authentication related setting for the website.
IIS anonymous authentication is in disabled state by default.
Change the Anonymous Authentication settings to Enabled for Default Web site MS_DP_SMSPKG$
This will fix issue of downloading package.
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