It seems that for some reason RadControls have remained deployed on your SharePoint server. You have two options to uninstall the web parts. The first one is to follow the manual uninstall steps described in the Installation and Deployment
article in the documentation.
The second option is to uninstall RadControls using the SharePoint 2010 Central Administration:
- Open SharePoint 2010 Central Administration;
- Navigate to System Settings -> Manage farm solutions;
- Click on the RadControls solution;
- Select Retract Solution and follow the steps;
- After you finish return to the page with the solutions and click on the RadControls solution again;
- Select Remove Solution;
Now you can try to run the installer again.
the Telerik team
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