Error Msg : the name <textblock> does not exist in the current context

Question

I have this in XAML section:

<TextBlock x:Name="txtBlkVATtotal" HorizontalAlignment="Left" Margin="1033,484,0,0" TextWrapping="Wrap" Text="TextBlock" Grid.Row="0" VerticalAlignment="Top" Height="38" Width="161"/>

When I try to reference in code behind, I got above error Message.  I had tried,Build : build, rebuild and clean solution but still can solve. 

Your help is appreciated.

Thanks