SelectedValue 失效

/// <summary>
        /// 绑定代表下拉选项
        /// </summary>
        public void BindOwnerDataII(string unitId, string bindid)
        {

            BaseCore obj = new BaseCore();
            DataTable dt = obj.GetOwnerByBusiness(unitId);
            this.ddlOwner.DataSource = dt;
            this.ddlOwner.DataTextField = "fullname";
            this.ddlOwner.DataValueField = "systemuserid";
            this.ddlOwner.DataBind();
            this.ddlOwner.SelectedValue = bindid; //这个放在前面,好像没有问题,
            this.ddlOwner.Items.Insert(0, new ListItem("全部", "00000000-0000-0000-0000-000000000000"));
           this.ddlOwner.SelectedValue = bindid; //这个放在后面,就有问题了. 
}