I had an issue this week where some SCCM 2012 R2 client machines were failing to download software installations. The download would start, get part of the way through, and then fail.
Looking in CAS.log, there were some strange errors, including some 0x80070020 errors. Unfortunately I didn’t catch a screenshot of the exact error message, but my research eventually led me to investigate our anti-virus exclusions.
As it turns out, our OfficeScan anti-virus server had some issues applying our custom exclusion lists to some of the more recently installed clients, of which my PC was one. I fixed the exclusions on the AV server, and then retried the installation. Success! The software that had previously failed to install, installed perfectly.
To conclude: Ensure that %windir%ccmcache is excluded from your virus scanner’s realtime scan.