Dealing with Error Code 1603 for .NET 3.5 Deployments
This blog post has some tips. If you produce a verbose log file during the .NET 3.5 update, it would help in debugging the situation. I have to state that for this issue, it would be best if you contact Microsoft Support through whatever support channels you typically use. Until then try the following scenarios
Option 1
Try installing as a ‘local admin’ not a ‘domain admin’. There have been isolated issues where 3.5 will not install properly unless done with local administrator privileges.
Option 2
1. Run the .net cleanup utility from https://astebner.sts.winisp.net/Tools/dotnetfx_cleanup_tool.zip
2. Make sure there are no .Net versions from add/remove programs
3. renamed the C:\Windows\Asssembly folder and restart
4. On restart, install the .Net Framework 3.5 from the linkhttps://download.microsoft.com/download/6/0/f/60fc5854-3cb8-4892-b6db-bd4f42510f28/dotnetfx35.exe
Reference Blog:
https://blogs.msdn.com/astebner/archive/2004/11/10/255346.aspx