What could be causing a button in XAML to not be clickable?

I have a button that works in other places within the page. If I add it to a particular grid though, it gets displayed but it's not clickable. Here's my full markup for that:

<Grid Style="{StaticResource NogMasterPageGridStyle}">
    <Grid.RowDefinitions>
        <RowDefinition Height="140"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>

    <!-- Page title -->
    <Grid Grid.Row="0">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="120"/>
            <ColumnDefinition Width="300"/>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="15"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="20"/>
            <RowDefinition Height="100"/>
            <RowDefinition Height="20"/>
        </Grid.RowDefinitions>
        // THIS BUTTON SHOULD BE CLICKABLE, AND IS ELSEWHERE
        <Button IsHitTestVisible="True" Grid.Column="0" Grid.Row="1" Canvas.ZIndex="9999" Content="Go Back" Style="{StaticResource NogButton}" 
                            Click="Click_GoBack"/>
        <StackPanel Grid.Column="1" Grid.Row="1" Grid.RowSpan="2" Orientation="Vertical" Margin="40,0,0,0">
            <Image Style="{StaticResource NogLogoImage}" VerticalAlignment="Center"></Image>
            <TextBlock Text="NOG"  Style="{StaticResource NogPageTitle}"  
                    IsHitTestVisible="false" TextWrapping="NoWrap" Margin="2,-35,0,0" HorizontalAlignment="Center"/>
        </StackPanel>
    </Grid> 

What could be causing the button to not be clickable in this particular grid?