Error when I cast a block

Hello,
In my plugin, i want to know if the player interact with a sign. So, this my code:

Code:

public void onPlayerInteract (PlayerInteractEvent event) {
        if(event.hasBlock()) {
            Block block = event.getClickedBlock();
            if(block.getTypeId() == 63) {
                Sign signe = (Sign)block;
                String[] txt = signe.getLines();
                event.getPlayer().sendMessage(txt[0]);
            }
        }
    }

But When in game, I interact with a sign, i have this error:

ClassCastException: org.getspout.spout.block.spoutcraftblock cannot be cast to org.bukkit.block.sign.

I have spout on my server but the plugin doesn't use spoutAPI, it's strange...

Thank you for your answers.

 

... (Sign)block.getState(); ...

 

Thank you very much, it works perfectly.