Hi, 

I just migrated a solution from VS2010 to VS2012, and an exception occurs when I use the designer of VS2012 to create controls in my radForms: 
System.Runtime.InteropServices.COMException (0x8004D745): A reference to the component 'Telerik.WinControls.UI' already exists in the project.

The exception occurs only when creating RadControls by drag and dropping from the toolBox, when I add Groups to a RadRibbon by clicking on "Add new Group", it works fine.
It also works fine when I add Windows Forms controls, the problem only occurs with Telerik Controls.

I tried under VS2010 and there is no exception raised.

I didn't get the problem when i used VS2010, so is there something special to do when migrating solutions from VS2010 to vs2012 ?

ps : see the attached file to get a more complete stacktrace.

Hello,

As described in your corresponding support thread, I would recommend to ensure that the same version of our controls is loaded in the toolbox and referred in your project.

To do this, please follow the steps bellow:

1. Open the Configure Wizard (documentation: http://www.telerik.com/help/winforms/installation-deployment-and-distribution-vsx-creation-and-configuration-wizard.html) and check the version of the distribution used by the project
2. Start the Toolbox Configurator (documentation: http://www.telerik.com/help/winforms/installation-deployment-and-distribution-vsx-toolbox-configurator.html) and ensure that the same version in loaded in the toolbox

Kind regards,
Chavdar,
the Telerik team