Type OnPlatForm not found

Hello,

I have this exception on my App.xaml: _Xamarin.Forms.Xaml.XamlParseException: Position 62:5. Type OnPlatForm not found in xmlns http://xamarin.com/schemas/2014/forms

My XAML with exception is:

            <!-- ______________________________________________________________________ -->
            <!-- Cross Platform adjustment -->
            <OnPlatForm x:Key="PickerAndEntryHeight"
                        x:TypeArguments="x:Double"
                        iOS="30"/>
            <!-- ______________________________________________________________________ -->
            <!-- Controls Hack -->
            <Style TargetType="Entry">
                <Setter Property="HeightRequest" Value="{DynamicResource PickerAndEntryHeight}"/>
            </Style>
            <Style TargetType="Picker">
                <Setter Property="HeightRequest" Value="{DynamicResource PickerAndEntryHeight}"/>
            </Style>
            <Style TargetType="DatePicker">
                <Setter Property="HeightRequest" Value="{DynamicResource PickerAndEntryHeight}"/>
            </Style>

Why i have an exception whereas this XAML works

            <!-- ______________________________________________________________________ -->
            <!-- Cross Platform adjustment -->
            <OnPlatform x:Key="FormLabelStyleMargin"
                        x:TypeArguments="Thickness"
                        WinPhone="0,10,0,-10"
                        Android="0,10,0,-10"
                        iOS="0,10,0,2"/>

            <!-- ______________________________________________________________________ -->
            <!-- Controls Style -->
            <Style TargetType="Label" x:Key="FormLabelStyle">
                <Setter Property="FontSize" Value="12"/>
                <Setter Property="TextColor" Value="{DynamicResource FormLabelTextColor}"/>
                <Setter Property="Margin" Value="{DynamicResource FormLabelStyleMargin}"/>
            </Style>

Anyone has idea? @NMackay ? @ClintStLaurent ?

Best regards