I would recommend you to uninstall all versions of the Telerik UI for WinForms suite. Then, download
the latest purchased version from your account and install it.
Then, carefully check the references to all Telerik controls in your project and make sure that they are the same version considering the suffix as well (.20 or .40). Better yet, you can remove all references and add them anew by using the DLLs from your fresh installation. Delete the license.licx file. After that, you should rebuild your project, close Visual Studio and open it again to make sure that no references are kept in the memory by Visual Studio.
The following help article demonstrates how to ensure that you are using a purchased version, not a trial one: https://docs.telerik.com/devtools/winforms/licensing/trial-vs-licensed-version
I hope this information helps. If you need any further assistance please don't hesitate to contact me.
Dess | Tech Support Engineer, Sr.
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