Input string was not in a correct format) with ExecuteReader (1 reply)

I am getting Input string was not in a correct format with the following code:

sql_connection = new MySqlConnection(ConfigurationManager.ConnectionStrings["SQLdb"].ConnectionString);
sql_connection.Open();

sql_command = new MySqlCommand("sp_check_if_member_exist", sql_connection);
sql_command.CommandType = CommandType.StoredProcedure;
sql_command.Parameters.AddWithValue("param_member_id", MySqlDbType.Int32).Value = Convert.ToInt32(Request.QueryString["id"]);
sql_command.Parameters.AddWithValue("param_member_guid", MySqlDbType.VarChar).Value = Convert.ToString(Request.QueryString["guid"]);
sql_command.Parameters.Add("param_is_exist", MySqlDbType.Bit).Direction = ParameterDirection.Output;

sql_reader = sql_command.ExecuteReader();
sql_reader.Read();

if (sql_reader.HasRows)
{
if (Convert.ToBoolean(sql_command.Parameters["param_is_exist"].Value) == true)
{
// prompt for activation; panelMessage.Visible = false;
panelActivation.Visible = true;
}
else
{
panelActivation.Visible = false;
lblMessage.Text = "Error activating your membership!";
panelMessage.Visible = true;
return;
}
}


The error occurs on this line:

sql_reader = sql_command.ExecuteReader();


where is my mistake?