At this point, the namespace Harmony.Web.Pages.WordMergeTemplateEdit is defensively not part of the Telerik.Web.UI assembly, neither of any other Telerik products.
Therefore, I can only make guesses from where this namespace comes from and why in your project is associated to the RadEditor.
I suggest double checking if the references are OK and that the needed Telerik assemblies are properly added to the project. Also, the ASP.NET page is properly configured with the proper page directives.
I suggest trying to follow the getting started article
from scratch and define why and how this namespace leads to the collision.
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