DDU not running. Launching main window failed error

[gamertwo1]

Sadly, I can't help much.
The error is quite clear on your screenshot: .NET can't find the file PresentationFramework-SystemXml.dll This is a core file of the .NET FrameWork.

Do you have some .net files here : C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5\System.Xaml.dll

Have you changed the c:\ to another name?

Yes files are there. And I haven't renamed or changed anything.

[Wagnard]

Do you also have PresentationFramework-SystemXml.dll in all of theses folders?

C:\Windows\Microsoft.NET\assembly\GAC_MSIL\PresentationFramework-SystemXml\v4.0_4.0.0.0__b77a5c561934e089
C:\Windows\Microsoft.NET\Framework\v4.0.30319\WPF
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\WPF

[gamertwo1]

Do you also have PresentationFramework-SystemXml.dll in all of theses folders?

C:\Windows\Microsoft.NET\assembly\GAC_MSIL\PresentationFramework-SystemXml\v4.0_4.0.0.0__b77a5c561934e089
C:\Windows\Microsoft.NET\Framework\v4.0.30319\WPF
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\WPF

yes