Problem disposing of socket / finalising twice?

public class Foo
{
    private Socket sock = null;
    private Thread tListenerThread = null
    private bool bInitialised;
    private Object InitLock = null;
    private Object DeInitLock = null;

    public Foo()
    {
    	bInitialised = false;

    	InitLock = new Object();
    	DeInitLock = new Object();
    }

    public bool initialise()
    {
    	if (null == InitLock)
    		return false;

    	lock (InitLock)
    	{
    		if (bInitialised)
    			return false;

    		sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
    		sock.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.MulticastTimeToLive, 8);
    		sock.Bind( /*localIpEndPoint*/);
    		sock.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.AddMembership, new MulticastOption(mcIP));

    		tListenerThread = new Thread(new ThreadStart(listener));
    		tListenerThread.Start();

    		bInitialised = true;
    		return true;
    	}
    }

    ~Foo()
    {
    	if (bInitialised)
    		deInitialise();
    }

    private void deInitialise()
    {
    	if (null == DeInitLock)
    		return;

    	lock (DeInitLock)
    	{
    		if (bInitialised)
    		{
    			sock.Shutdown(SocketShutdown.Both); //throws System.ObjectDisposedException
    			sock.Close();

    			tListenerThread.Abort(); //terminates xunit test!
    			tListenerThread = null;

    			sock = null;

    			bInitialised = false;
    		}
    	}
    }
}