Error 10 Delegate 'System.Action'

Action<string> messagetarget;
messagetarget = delegate(string s) { showmessage(s); };
//this.Invoke(messagetarget);

public void showmessage(string thid1)
{
    lvc[0] = DateTime.Now.Hour + ":" + DateTime.Now.Minute + ":" + DateTime.Now.Second;
    lvc[1] = thid1;
    listView2.Items.Add(new ListViewItem(lvc, 0));
}

    Action<string> messagetarget;
    messagetarget = delegate(string s, string t) { showmessage(s, t); };
    this.Invoke(messagetarget);

public void showmessage(string thid1,string message1)
{
    lvc[0] = DateTime.Now.Hour + ":" + DateTime.Now.Minute + ":" + DateTime.Now.Second;
    lvc[1] = thid1;
    lvc[2] = message1;
    listView2.Items.Add(new ListViewItem(lvc, 0));
}