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Since Q1 2012 our automatic installer (msi) provides only Silverlight 5 controls. If you need to use the latest Silverlight 4 controls, the only option is to download a hotfix (zip) with the Silverlight 4 controls.
In order the take advantage of the VSExtensions, you can unzip the hotfix package in %appdata%\Telerik\Updates keeping the containing folder, e.g. you should get %appdata%\Telerik\Updates\RadControls_for_Silverlight4_2012_1_0215_DEV_hotfix. This will help the extensions to detect the Silverlight 4 distribution automatically. Design time should work as well.
Having SL4 distribution in the correct folder on your machine, makes possible to update your projects to the latest version using the Upgrade Wizard
(it will automatically detect the appropriate distribution according the project's silverlight version).
If you use the Visual Studio Toolbox for SL4 and SL5 projects, you should change the currently loaded distribution in the Toolbox using the Toolbox Configurator
when switching between different projects. When developing Silverlight 4 application the Toolbox should be configured to list Silverlight 4 distribution. Please, note that the Silverlight 4 distributions are versioned *.1040 and Silverlight 5 distributions are versioned *.1050.
I hope this will help. Let me know if I can be of further assistance.
the Telerik team
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