WPF Copy Paste command Issue

HI,

I have copy paste button like this. Whenever I select some text, this copy button is becoming active. Which is correct behavior.

<Button Name="CopyButton" Grid.Row="0" Grid.Column="1" VerticalAlignment="Top" Margin="6,6,3,0"  ToolTip="{x:Static res:Controls.Copy}"  Command="ApplicationCommands.Copy">
       <Image Source="../Resources/Images/GenericEditorActions/Copy.png" x:Name="CopyImage"/>
 </Button>

Now my question is, I have one textbox in my application. Above Copy button should always be in in-active state even I select Text from that textbox. As per req. that textbox should not support any copy paste functionality.

How would I do that?

Pls help

Dee