.NET Framework 3.5 installation failed for component RGB Rast (error 643)

When you try to install Microsoft .NET Framework 3.5 Service Pack 1 and .NET Framework 3.5 Family Update for .NET versions 2.0 through 3.5 it can fail. If you look into C:\Windows\WindowsUpdate.log you will see the following error message

Handler :::::::::::::
Handler :: START :: Handler: Command Line Install
Handler :::::::::
Handler : Updates to install = 1
Handler : WARNING: Command line install completed. Return code = 0x00000643, Result = Failed, Reboot required = false
Handler : WARNING: Exit code = 0x8024200B
Handler :::::::::
Handler :: END :: Handler: Command Line Install
Handler :::::::::::::
Agent *********
AU Can not perform non-interactive scan if AU is interactive-only
Agent ** END ** Agent: Installing updates [CallerId = MicrosoftUpdate]
Agent *************
COMAPI >>– RESUMED — COMAPI: Install [ClientId = MicrosoftUpdate]
COMAPI – Install call complete (succeeded = 0, succeeded with errors = 0, failed = 1, unaccounted = 0)
COMAPI – Reboot required = No
COMAPI – WARNING: Exit code = 0x00000000; Call error code = 0x80240022
COMAPI ———
COMAPI — END — COMAPI: Install [ClientId = MicrosoftUpdate]
COMAPI ————-

Or, if you click on the error log link on the last screen of the .NET installation, you will see these two lines:

RGB Rast: [2] Error: Installation failed for component RGB Rast. MSI returned error code 1603
WapUI: [2] DepCheck indicates RGB Rast is not installed.

If you search for these error messages in the internet, you can find the recommendation to run RGB Rast installation alone. How to find it? Just extract the dotnetfx v3.5 SP1.exe file and find the installation file (RGB9RAST_x64.msi or RGB9RAST_x86.msi) down here:
..\wcu\dotNetFramework\dotNetFX30

Sometimes it helps and you need just to run the full installation then. Sometimes it does not and you’ve got the message

User installations are disabled via policy

Easy to fix, isn’t it?

1. Run GPEDIT.MSC
2. Go to Computer Configuration\Administrative Templates\Windows Components\Windows Installer
3. Find the Prohibit User Installs value and set it up to Disabled.
   Close GPEDIT and run the installation again

Still does not work?

Well, it did not change the registry.
Run REGEDIT
Go to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\windows\Installer
Create the DWORD:DisableUserInstalls value if it does not exist and set it up to 0.

Now you will be able to install .NET 3.5

Do not forget to return your changes in GPEDIT and REGEDIT back to what you had before