access数据库+PagedDataSource给gridview分页

我用的是access数据库，然后分页是时候用到了PagedDataSource。
他老是报错“异常信息: 无法计算未实现 ICollection 的数据源中的计数。”        private int PageNo
        {
            get { return (int)ViewState["page"]; }
            set { ViewState["page"] = value; }
        }        /// <summary>
        /// 设置分页
        /// </summary>
        private void SetDataBind()
        {
            PagedDataSource pds = new PagedDataSource();
            pds.AllowPaging = true;
            pds.PageSize = 5;
            pds.CurrentPageIndex = (int)ViewState["page"];
            pds.DataSource = (DataSetDefines.RiskInfoDataTable)ViewState["list_risk"];
            dgvRisk.DataSource = pds;
            ViewState["LastNo"] = pds.PageCount;报错
            dgvRisk.DataBind();
        }        private void Enablbt()
        {
            if (PageNo == 0)
            {
                this.lbtFirst.Enabled = false;
                this.lbtUp.Enabled = false;
                this.lbtDown.Enabled = true;
                this.lbtLast.Enabled = true;
            }
            else if (PageNo == (int)ViewState["LastNo"] - 1)
            {
                this.lbtFirst.Enabled = true;
                this.lbtUp.Enabled = true;
                this.lbtDown.Enabled = false;
                this.lbtLast.Enabled = false;
            }
            else
            {
                this.lbtFirst.Enabled = true;
                this.lbtUp.Enabled = true;
                this.lbtDown.Enabled = true;
                this.lbtLast.Enabled = true;
            }
        }        protected void lbtFirst_Click(object sender, EventArgs e)
        {
            PageNo = 0;
            SetDataBind();
            Enablbt();
        }        protected void lbtUp_Click(object sender, EventArgs e)
        {
            PageNo--;
            SetDataBind();
            Enablbt();
        }        protected void lbtDown_Click(object sender, EventArgs e)
        {
            PageNo++;
            SetDataBind();
            Enablbt();
        }        protected void lbtLast_Click(object sender, EventArgs e)
        {
            PageNo = (int)ViewState["LastNo"] - 1;
            SetDataBind();
            Enablbt();
        }