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When installing SQL Server Management Studio on top of an existing SQL Server 2008 or SQL Server 2008 R2 installation, the setup program may fail with the following .NET Framework exception, even if the .NET Framework 3.5 and 4.0 is already installed on the target machine:

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 Settings\[UserAccountName]\Local Settings\Application Data\Microsoft_Corporation\LandingPage.exe_StrongName_ryspccglaxmt4nhllj5z3thycltsvyyx\10.0.0.0\user.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.
File name: 'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'
   at System.Configuration.TypeUtil.GetTypeWithReflectionPermission(IInternalConfigHost host, String typeString, Boolean throwOnError)
   at System.Configuration.RuntimeConfigurationRecord.RuntimeConfigurationFactory.Init(RuntimeConfigurationRecord configRecord, FactoryRecord factoryRecord)
   at System.Configuration.RuntimeConfigurationRecord.RuntimeConfigurationFactory.InitWithRestrictedPermissions(RuntimeConfigurationRecord configRecord, FactoryRecord factoryRecord)
   at System.Configuration.RuntimeConfigurationRecord.RuntimeConfigurationFactory..ctor(RuntimeConfigurationRecord configRecord, FactoryRecord factoryRecord)
   at System.Configuration.RuntimeConfigurationRecord.CreateSectionFactory(FactoryRecord factoryRecord)
   at System.Configuration.BaseConfigurationRecord.FindAndEnsureFactoryRecord(String configKey, Boolean& isRootDeclaredHere)

Resolution

Delete the offending user.config file in the following directory:

    C:\[UserAccountName]\AppData\Microsoft_Corporation\
    LandingPage.exe_StrongName_ryspccglaxmt4nhllj5z3thycltsvyyx\10.0.0.0\

Restart the installer and note that the deleted configuration file will be recreated with corrected settings for the System.Configuration assembly’s version number.

Resources

A similar error and its resolution was posted on MSDN Blogs. Standalone installers for the 32- and 64-bit versions of SQL Management Studio Express for SQL Server 2008 R2 Express can be found on the Microsoft Express Database download page.