If the web installer fails to retrieve vs_preclean_vs.exe , download the complete for your Visual Studio 2012 edition. The ISO contains the packages\VS_Clean\VS_PreClean_vs.exe file and does not rely on an internet connection to fetch it.

: Right-click the installer and set it to run in Compatibility Mode for Windows XP (Service Pack 3).

It is by developers — it’s invoked automatically by the build system.