Hi Fabio,
You need to make sure that you use the right .resx file for the Telerik.Web.UI assembly. In your case you use an older version of the .resx files compared to the version of the Telerik.Web.UI assembly. To be sure, I recommend you to copy the Telerik.Web.UI.dll and the .resx files from the Telerik.Web.UI_<VERSION>.zip file.
Best wishes,
Fiko
the Telerik team
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