Thank you for contacting us.
I guess that for some reason the toolbox wasn't updated and that is why you get the version error. You can use the Toolbox Configurator
for checking which version of the controls is populated in the Visual Studio's toolbox. If the toolbox is populated with an older version of the controls, choose the version 2011.2.915.40 from the drop down list and press 'Finish'. The operation requires Visual Studio restart.
I hope this will solve your issue. Please, do not hesitate to write us again if you need any further assistance.
the Telerik team
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