System.Configuration.ConfigurationErrorsException: An error 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:Documents and SettingsBoschRLocal SettingsApplication DataMicrosoft_CorporationLandingPage.exe_StrongName_ryspccglaxmt4nhllj5z3thycltsvyyx10.0.0.0user.config line 5) ---> System.IO.FileNotFoundException: 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.When installing SQL Server 2008 R2 on a Windows XP (or, according to the comments, Windows 7) development machine that has been around for quite some time, I got an error stating an unhandled exception occured in the application (see image). The error showed up directly upon startup and read:

An error 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.

Repairing the .NET 4.0 framework didn’t solve the issue. Neither did removing all SQL stuff through ‘Add or Remove Programs’. Looking into the error a bit further…

 The system cannot find the file specified. (C:Documents and Settings_USERNAME_Local SettingsApplication DataMicrosoft_CorporationLandingPage.exe_StrongName_ryspccglaxmt4nhllj5z3thycltsvyyx10.0.0.0user.config line 5) —> System.IO.FileNotFoundException: 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.

 So the problem probably wasn’t that System.dll couldn’t be found, but some user.config file for the landingpage executable. The solution is as simple as it is radical: remove the entire (temporary) folder ‘C:Documents and Settings_USERNAME_Local SettingsApplication DataMicrosoft_Corporation’ (where USERNAME_ is, of course, the current username). After this the setup should start up without any problems.