It seems there is some mismatch of the used assemblies, please note that all the referenced Telerik dlls in the project should be of the same version and from the same location. I suggest that you try the following steps:
- Open your application and remove all Telerik's references.
- Save the project and close it.
- Open the project directory and delete "Bin" and "Obj" folders.
- Open the project and add the references again.
- Rebuild the application.
I hope doing this will help you resolve the issue.
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