There was a problem a while back with some of the .NET updates repeatedly failing to install:

I also had problems a while back with installation of a number of updates. After lots of searching on the MS site I found a script file that repairs registry settings and everything apparently installed properly after running that. I've used it a couple of times since then. These latest .NET updates also wouldn't install for me so I ran that script again and that seems to have solved the problem.

I can't remember now where on the MS site I found the script but think it was associated with an MS Word installation problem.

The script is at the end of this post. To use it copy into notepad and save, then replace the "txt" extension with "cmd". Double click that file and sit back. I don't understand any of what it is doing, so user beware!

cd /d "%ProgramFiles%\Windows Resource Kits\Tools"
subinacl /subkeyreg HKEY_LOCAL_MACHINE /grant=administrators=f /grant=system=f
subinacl /subkeyreg HKEY_CURRENT_USER /grant=administrators=f /grant=system=f
subinacl /subkeyreg HKEY_CLASSES_ROOT /grant=administrators=f /grant=system=f
subinacl /subdirectories %SystemDrive% /grant=administrators=f /grant=system=f
subinacl /subdirectories %windir%\*.* /grant=administrators=f /grant=system=f
secedit /configure /cfg %windir%\repair\secsetup.inf /db secsetup.sdb /verbose