To use this attribute it's necessary to inherit a class from Unique base course-initializer or utilize a static helper system: So your DataContext for "video_length_textbox" is set to itself, plus your IncrementingTextBox course doesn't have a community property named ConfigurationModel OldCurmudgeonOldCurmudgeon 66k1818 gold badges126126 silver badges220220 bronze badges 8 1 https://elancommercialprojects.blogspot.com