Your problem is that Widgets does not support Views as you can see here. In your case, you could replace that View by a LinearLayout like this:
<LinearLayout
android:id="@+id/widget_horizontal_white_bar"
android:layout_width="fill_parent"
android:layout_height="3dip"
android:layout_marginLeft="20dp"
android:layout_marginRight="20dp"
android:layout_marginTop="6dp"
android:background="#FFFFFF"
android:orientation="horizontal" >
</LinearLayout>