Did you get any other updates with this one and did they install okay ?
You could try a direct download from the MS Update Catalog if that hasn't been tried already.
http://www.catalog.update.microsoft.com/Search.aspx?q=KB2934520Yours is the second one.
No doubt they will have tried the Update troubleshooter, the dism /restorehealth and sfc /scannow commands ?
Did the MS tech run the repair program's Pre-Scan to see if there was any Package corruption ?
This would also show up in a sfc /scannow as not being able to repair some files.
What sometimes works if the direct download doesn't, is to install all but the .NET Framework ones and leave those until last.
Looking at the release date for that update, you probably no longer have a restore point that will take you back to before they were installed, but if you have - use it to go back then install all but that that one and then see if it will install.