Hi Helen,
Unfortunately, we don't have such example, demonstrating how to use RadComboBox in DataForm.
I would suggest you to refer to the following forum thread - http://www.telerik.com/community/forums/silverlight/combobox/radcombobox-within-dataform-did-not-apply-changes-after-committed.aspx
I hope this helps.
Regards,
George
the Telerik team
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