为什么oledb这样不能连接dbf

Question

string strDirectory;
strDirectory=textBox1.Text.Trim();
OleDbConnection myConn; //数据连接
string    myStrConnection="Provider=Microsoft.Jet.OLEDB.4.0;Data Source="+strDirectory+"";
string myStrSelect="Select 克数 FROM "+strDirectory+""; myConn = new OleDbConnection(myStrConnection);
myConn.Open();
OleDbDataAdapter myAdapter =new OleDbDataAdapter(myStrSelect,myConn);
OleDbCommandBuilder custCB = new OleDbCommandBuilder(myAdapter);
DataSet myDs=new DataSet();
myAdapter.Fill(myDs,"aa");
         myAdapter.Update(myDs,"aa");
myConn.Close();
Application.Exit();