Help! Error occur when try to open oracle connecion in c#. Thanks!

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C#

Oracle

System.Data.OracleClient requires Oracle client software version 8.1.7 or greater. That error occur when it try to do con.open().
The code is written in VS2008.
Oracle DB runs on the linux system in the VMware Workstation which is installed on my machine.
(PS: I connect to the Oracle DB successfully using pl/sql developer software).
Pls help, thanks.
The code is:

public void TestReturnProcedureWithReturnValue()
{
    OracleConnection con = new OracleConnection();
    con.ConnectionString = ConnectionString;
    OracleCommand cmd = new OracleCommand();
    cmd.CommandText = "sp_pro9";
    cmd.CommandType = System.Data.CommandType.StoredProcedure;
    cmd.Connection = con;
    cmd.Parameters.Add(new OracleParameter("spNo", 10));
    OracleParameter cursor = new OracleParameter();
    cursor.ParameterName = "p_cursor";
    cursor.OracleType = OracleType.Cursor;
    cursor.Direction = System.Data.ParameterDirection.Output;

    cmd.Parameters.Add(cursor);

    try
    {
        con.Open();
        cmd.ExecuteScalar();
    }
    catch (Exception e)
    {
    }
    finally
    {
        con.Close();
    }



}