Thank you for writing.
We are aware of an issue that is related to the Silverlight Pivot control which causes the OnApplyTemplate() method to be called twice on controls. The first time it is called, no template children can be resolved for unclear reasons and if a property is set before the second OnApplyTemplate() call is made, the controls will not function properly because the ControlTemplate has not yet provided the necessary template parts, that is, the control is not in a valid state yet. The only thing that we could do on our side is to suppress the exception so that there are no error messages in Blend or Visual Studio but the control may still not work properly.
In order to set the text for the buttons you must use the localization features of RadControls for WP7. The buttons text is a localizable resource and is therefore specified by external resource files(or through code) which provide values for their specific culture. Please have a look at the online documentation for details. What you will need to provide are values for the OkButtonText and CancelButtonText keys.
Please write again if you need further assistance.
the Telerik team
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