错误的值作为参数传递

我遇到的问题是,脚本运行时似乎不考虑参数值。我不难理解的是,Debug.Print()方法显示正确的值,但是Access db中的存储过程未按该值进行选择,而是返回SELECT语句的结果,而不受引用传递的参数值的任何限制。怎么了 ? Srcipt应该填写赢表应用程序的datagridview。

...

private void pbSearchDepartment_Click(object sender, EventArgs e)
{
using(OleDbCommand comDeptTotals=conAcc.CreateCommand())
{       
OleDbDataAdapter da = new OleDbDataAdapter();
DataTable dt = new DataTable();
comDeptTotals.CommandText = "sp_ShowDepartmentTotals";
comDeptTotals.CommandType = CommandType.StoredProcedure;
Debug.Print(cbDepartments.SelectedItem.ToString());
comDeptTotals.Parameters.AddWithValue("Area", cbDepartments.SelectedItem);

conAcc.Open();


da.SelectCommand = comDeptTotals;
da.SelectCommand.ExecuteNonQuery();
da.Fill(dt);
Debug.Print(dt.Rows.Count.ToString());

dgv_NAV_TOTALS.DataSource = dt.DefaultView;
}
}
}
}

...