System.Configuration.ConfigurationErrorsException: An error occurred creating the configuration sect

An error has occurred creating the configuration section handler for userSettings/Microsoft.SqlServer.Configuration.LandingPage.Properties.Settings: Could not load file or assembly 'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' or one of its dependencies. The System cannot find the file specified. (C:\Users\Billy\AppData\Local\Microsoft_Corporation\LandingPage.exe_StrongName_ryspccglaxmt4nhllj5z3thcyltsvyyx\10.0.0.0\user.config line

If you are running Windows 7, read on.

Whilst I'm fully aware that this answer is around a year too late, I thought it might be useful for someone.

Assuming you've already:

Step 1: Download and install Microsoft .Net Framework 3.5 SP1. 

Step 2: Download and install Windows Installer 4.5.

and it hasn't worked (It didn't for me, or most others with this problem), do the following:

Delete the "C:\Users\{Username}\AppData\Local\Microsoft_Corporation\" folder (Replace {Username} with Billy in the original posters case)

No idea why, but it works.

And yes - This IS a serious solution :-)