I am making a code to move the elements of a list box up and down. For that, I have made two buttons to move the element up (Move Up button) and down (Move Down button). Here is my code:

```
if (m_lbOPFfiles.SelectedIndex != m_lbOPFfiles.Items.Count && m_lbOPFfiles.SelectedIndex != -1)
        {
            ListItem item = m_lbOPFfiles.SelectedItem;
            int index = m_lbOPFfiles.SelectedIndex;
            m_lbOPFfiles.Items.RemoveAt(index);
            lstResdetails.Items.Insert(index + 1, item);
         }

```

Now I am getting the namespace error for ListItem. Can anyone help me rectify it?