This example demonstrates how to configure lightweight GridViewComboBoxColumn with validation.
Validation rules:
- ItemKey can not be 0
- CustomerItem can not be empty

See also:
WPF: http://docs.telerik.com/devtools/wpf/controls/radgridview/columns/columntypes/column-types-combobox-column 
SL: http://docs.telerik.com/devtools/silverlight/controls/radgridview/columns/columntypes/column-types-combobox-column