this is the answer
but you must ignore the exceptions
try
{
listBox2.Items.Add(listBox1.SelectedItem);
listBox1.Items.Remove(listBox1.SelectedItem);
listBox1.ClearSelected();
}
catch(Exception ee){}
try
{
listBox1.Items.Add(listBox2.SelectedItem);
listBox2.Items.Remove(listBox2.SelectedItem);
listBox2.ClearSelected();
}
catch(Exception ee){}
let me know if you have any question with code