A TwoWay or OneWayToSource binding cannot work on the read-only property for same name property from different page

Question

I have two pages TunerPage.xaml and FormCameraSetting.xaml, and FormCameraSetting in TunerPage as Frame through binding, like this:

TunerPage.xaml

<Grid>
    <Grid.ColumnDefinitions>
         <ColumnDefinition Width="300"/>
         <ColumnDefinition/>
    </Grid.ColumnDefinitions>
    <UniformGrid Grid.Column="0" Rows="1" Columns="2">
        <Label Content="Shutter" FontFamily="Arial" Foreground="White" VerticalContentAlignment="Center"/>
        <TextBox Style="{StaticResource TextBoxStyle1}" Text="{Binding Shutter, Mode=OneWay}" HorizontalContentAlignment="Center" VerticalContentAlignment="Center" IsEnabled ="False"/>
    </UniformGrid>
    <Frame Grid.Column="1" Content="{Binding PageDisplay}" NavigationUIVisibility="Hidden" Loaded="Frame_Loaded" Unloaded="Frame_Unloaded"/>
</Grid>

FormCameraSetting.xaml

<Grid>
    <Grid.ColumnDefinitions>
         <ColumnDefinition Width="300"/>
         <ColumnDefinition/>
    </Grid.ColumnDefinitions>
    <Label Content="Shutter" FontFamily="Arial" Foreground="White" VerticalContentAlignment="Center"/>
    <TextBox HorizontalContentAlignment="Right" Style="{StaticResource TextBoxStyleForm2}" Text="{Binding Shutter, UpdateSourceTrigger=Explicit}"/>
 </Grid>

Both of them have TextBox. One in TunerPage.xaml is binding Shutter on TunerAction.cs and mode is Oneway. Another in FormCameraSetting.xaml is binding Shutter on CameraSettingViewModel.cs and mode is Twoway.

TunerAction.cs (ViewModel)

public double Shutter
{
    get 
    {
         return 2000; 
    }
}

CameraSettingViewModel.cs (ViewModel)

private double shutter;
public double Shutter
{
    get 
    {
        return shutter;
    }
    set
    {
        shutter = value;
    }
}

Now in xaml.cs, I set their DataContext equal to their ViewModel when the page loaded.

TunerPage.xaml.cs

public TunerAction tunerAction = new TunerAction();
public TunerPage()
{
    InitializeComponent();            
}
private void SettingPageBase_Loaded(object sender, RoutedEventArgs e)
{
    this.DataContext = tunerAction;
}

CameraSettingViewModel.xaml.cs

public CameraSettingViewModel viewModel = new CameraSettingViewModel();
public FormCameraSetting()
{
    InitializeComponent();
}
private void CameraSettingTemplate_Loaded(object sender, RoutedEventArgs e)
{
    this.DataContext = viewModel;
}

When I run VisualStudio, it shows an error:

But, if I change "Shutter" to another name in TunerAction.cs, or set DataContext after InitializeComponent() not when the page loaded, it will not cause this error.

Why did this error happen?

Thanks!