C# search in combobox

InvalidArgument=Value of '0' is not valid for 'index'.
Parameter name: index

void loadSubject(ComboBox cbo)
        {
            try
            {
                SqlConnection con = new SqlConnection(cs.getConnectionString());
                con.Open();
                DataTable dt = new DataTable();
                string query = "SELECT subjectcode,description FROM tblsubject WHERE description LIKE '%' + @1 + '%' ORDER BY description ASC";
                SqlCommand cmd = new SqlCommand(query, con);
                cmd.Parameters.AddWithValue("@1",cbosubject.Text);
                SqlDataReader dr = cmd.ExecuteReader();
                dt.Load(dr);
                cbo.DisplayMember = "description";
                cbo.ValueMember = "subjectcode";
                cbo.DataSource = dt;
            }
            catch (Exception)
            {
                publicFunctions.mBox(3, "error occured");
            }
        }

private void cbosubject_TextChanged(object sender, EventArgs e)
        {
            loadSubject(cbosubject);
        }