Hello.

I am using an Access database. Recently I learnt that it is not a good idea to pass information directly into an SQL query... and it is a good practice to use parameters instead.

Note1: rentChecked_cmd is an OleDBCommand object
Note2: I've already created the Parameter in InitialiseComponents() using the following statement:
rentChecked_cmd.Parameters.Add(new OleDbParameter("RentID", Integer));

Well, heres my code, I've kept it simple

private void returnBtn_Click(object sender, System.EventArgs e)
{
rentChecked_cmd.Parameters["RentID"].Value=int.Parse(whatever);

rentChecked_cmd.CommandText = "SELECT DateDue FROM Rents WHERE RentID=@RentID";

mainConn.Open();

reader = rentChecked_cmd.ExecuteReader();
...
...
...

}

When I click the "Return" button for the first time, everything works fine... but when I click it again.. the database tells me "Accessor is Invalid". After debuggined the error is throw by the
reader = rentChecked_cmd.ExecuteReader() line

This error is frustrating me cause I cant find any reason! Whats funny is that in my returnBtn_Click() method when I add the line "rentChecked_cmd.Parameters.Add(new OleDbParameter("RentID", Integer));"... it works... But thats so stupid, I am not supposed to Add a new Parameter each time a button is clicked!!