First, why did it take two months to find the problem? We're looking at a Patching 201-level screwup here, not rocket science.

If that's what actually happened with Error 80073712, it raises three disconcerting questions. We're talking about multiple official, released, and presumably supported versions of the same file. Note that we aren't talking about some mysterious third party or an application program that's diddling in places it shouldn't. That's where Error 80073712 raises its ugly head. Then some program - maybe the installer, maybe some other glue program - works fine with Version 2, but croaks with Version 3. But in unusual situations, the installer finds that Version 3 of A.DLL is already installed. If it hits Version 2, it goes on to the next installation task.

If the installer hits Version 1, it installs Version 2.

Almost all of the systems the installer encounters are either running Version 1 or Version 2 of A.DLL. The simplest analogous scenario calls for the KB 2919355 installer to install version 2 of A.DLL. Rather than overwriting a newer version of the file with an older version, it skips to the next installation task. When patching, the patch installer looks to see if it's being asked to install an 'old' version of a specific file. Problems arise when a program will work with, say, version 2, but won't work with version 3. The versions are typically identified by time/date stamps. Let's call the program A.DLL and the versions 1, 2 and 3. The basic scenario, which looks a whole lot like an old-fashioned 'DLL hell' problem, goes something like this: Microsoft releases three different versions of a program. I don't claim to have any inside information about this patch, but many of us have seen 'later file version' problems with patches before.

Windows 8 installer error