Custom Site Map Provider Caching Problem

[jgd123456]

Hi, i'm using my own sql server 2005 site map provider. The problem i have is that when i make a change to some of the data in the database it does not update the site map display (some cached version is displayed) unless i restart iis. Here's the code for my site map provider:

using System;
using System.Data;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Configuration;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public class MySqlSiteMapProvider : StaticSiteMapProvider
{
    private SiteMapNode _root = null;
    private Dictionary<int, SiteMapNode> _nodes = new Dictionary<int, SiteMapNode>(1000);

    public override void Initialize(string name, System.Collections.Specialized.NameValueCollection config)
    {
        base.Initialize(name, config);
    }

    protected override SiteMapNode GetRootNodeCore()
    {
        this.Clear();
        return this.BuildSiteMap();
    }

    public override SiteMapNode BuildSiteMap()
    {
        lock (this)
        {
            // If there is no root node, then there is no site map
            if (_root == null)
            {
                // Start with a clean slate
                this.Clear();

                // Add the root node
                _root = new SiteMapNode(this, "0", "/", "Home", "Home");
                this.AddNode(_root);

                // Now add the menu items
                this.AddMenuItems(null);
            }

            return _root;
        }
    }

    public void AddMenuItems(int? parentID)
    {
        foreach (MenuItemsItem menuItem in MenuItems.GetMenuItemsByParentID(parentID))
        {
            NameValueCollection attributes = new NameValueCollection();
            attributes.Add("ShowInNavigation", menuItem.ShowInNavigation.ToString());
            attributes.Add("ShowInSiteMap", menuItem.ShowInSiteMap.ToString());
            attributes.Add("ShowParentItems", menuItem.ShowParentItems.ToString());

            SiteMapNode node = new SiteMapNode(this, menuItem.MenuItemID.ToString(), menuItem.Path, menuItem.Title, menuItem.Title, null, attributes, null, null);
            _nodes.Add(menuItem.MenuItemID, node);
            this.AddNode(node, menuItem.ParentID == null ? _root : _nodes[(int)menuItem.ParentID]);

            // Now add the sub categories
            this.AddMenuItems(menuItem.MenuItemID);
        }
    }

    protected override void Clear()
    {
        lock (this)
        {
            _root = null;
            _nodes = new Dictionary<int, SiteMapNode>(1000);
            base.Clear();
        }
    }
}

Appreciate if someone could tell me what i am doing wrong.

Thanks