代码如下：
        private void Import()
        {
            openFileDialog1.CheckFileExists = true;  //验证路径有效性
            openFileDialog1.CheckPathExists = true; //验证文件有效性
            OpenFileDialog ofd = new OpenFileDialog();
            try
            {
                //if (open.ShowDialog() == DialogResult.OK)
                if(openFileDialog1.ShowDialog() ==DialogResult.OK)
                {
                    string  source = openFileDialog1.FileName;
                    this.Text = source;
                    string connstr = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" +source+";Extended Properties=dBASE IV;";
                    string sel = "select * from " + openFileDialog1.FileName;
                    OleDbCommand olecmd = new OleDbCommand(sel, new OleDbConnection(connstr));
                    OleDbDataAdapter olesda = new OleDbDataAdapter(olecmd);
                    DataSet ds = new DataSet();
                    olesda.Fill(ds);
                    this.dataGridView1.DataSource = ds.Tables[0];
                    ds.Dispose();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message.ToString(), "错误提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                return;
            }
        }

自定义一个方法把dbf文件导入datagridview，通过openfiledialog获得文件的路径了，但老是报错：请确认文件的有效性，和连接的问题？
大家帮我看一下，是代码的连接字符串有问题，还是有其他的问题？
再问一个问题，假如把dbf文件导入datagridview后，想要把datagridview的数据添加到SQL中，代码要改那里？