In my routine to load a treeview, I place a code on the tag which is the level and the node type code:

private void LoadTree()
{
    TreeNode oNode;

    oNode = treeView1.Nodes.Add("Customers");
    oNode.Tag = "0.customers";

    oNode = treeView1.Nodes.Add("Accounts");
    oNode.Tag = "0.accounts";
    oNode.Expand();

    foreach (csItem oItem in csAppStartup.oItems.colItems)
    {
        oNode.Nodes.Add(oItem.sCaption);
        oNode.Tag = "1." + oItem.sItemCode;
    }

}

Then in the Mouse up I want to read the tag of the selected node to see which item the user right-clicked on:

private void treeView1_MouseUp(object sender, MouseEventArgs e)
{

    if(e.Button == MouseButtons.Right)
    {
        TreeNode oNode = treeView1.SelectedNode;
        string sNodeInfo = oNode.Tag.ToString();

    }
}

On the last line I'm getting "Object reference not set to an instance of an object.".

Anyone see what's wrong?