Secuela:Error:Error:Table1 no está asociado a Table2

El problema es probablemente con la forma en que está configurando su asociación, mencione amablemente su estrategia.

Lo siguiente funciona bien si usa la configuración del archivo express index.js y luego consulta http://docs.sequelizejs.com/en/1.7.0/articles/express/

'use strict';
module.exports = function(sequelize, DataTypes) {
  var customer = sequelize.define('customer', {
    customernumber: DataTypes.STRING(30), //remove
    customerspecificationid: DataTypes.INTEGER,
    customertypeid: DataTypes.INTEGER,
    sportid: DataTypes.INTEGER,
    customername: DataTypes.STRING(20), //remove
    address: DataTypes.STRING(30),
    city: DataTypes.STRING(30),
    state: DataTypes.STRING(30),
    zipcode: DataTypes.STRING(30),
    ordercomplete: DataTypes.BOOLEAN,
    isactive: DataTypes.BOOLEAN
  }, {
      associate: function(models) {
          // associations can be defined here
        models.customer.hasMany(models.order);
      }
  });

  customer.hook('afterCreate', function(cust, options) {
      //generate the customer number

        return customer.update({ customernumber: custnumber }, {
        where: {
          id: cust.id
        }
      });
  });

  return customer;
};


'use strict';
module.exports = function(sequelize, DataTypes) {
  var order = sequelize.define('order', {
    ponumber: DataTypes.STRING(30), //remove
    orderdate: DataTypes.DATE,
    shippingmethod: DataTypes.STRING(30),
    shippingterms: DataTypes.STRING(30),
    deliverydate: DataTypes.DATE,
    paymentterms: DataTypes.STRING(30),
    overridediscount: DataTypes.BOOLEAN,
    shippingaddress: DataTypes.STRING(30),
    shippingcity: DataTypes.STRING(30),
    shippingstate: DataTypes.STRING(20),
    shippingzipcode: DataTypes.STRING(10),
    isactive: DataTypes.BOOLEAN
  }, {
      associate: function(models) {
        // associations can be defined here
        models.order.belongsTo(models.user);
        models.order.belongsTo(models.customer);
      }
  });

  order.hook('afterCreate', function(ord, options) {
      //generate po number

      return order.update({ ponumber: ponumbr }, {
        where: {
          id: ord.id
        }//,
        //transaction: options.transaction
      });
  });

  return order;
};

'use strict';

module.exports = function(sequelize, DataTypes) {
  var user = sequelize.define('user', {
    username: DataTypes.STRING(30), //remove
    password: DataTypes.STRING(255),
    emailaddress: DataTypes.STRING(255),
    firstname: DataTypes.STRING(30),
    middlename: DataTypes.STRING(30), //remove
    lastname: DataTypes.STRING(30),
    approve: DataTypes.BOOLEAN,
    roles: DataTypes.STRING(50),
    isactive: DataTypes.BOOLEAN
  }, {
    classMethods: {
      associate: function(models) {
        // associations can be defined here
        models.user.hasMany(models.order);
      }
    }
  });

  user.hook('afterCreate', function(usr, options) {
      //hash the password

      return user.update({ password: passwd }, {
        where: {
          id: usr.id
        }
      });
  });

  return user;
};

// archivo index.js donde deberás asociar las rutas

var fs        = require('fs')
    , path      = require('path')
    , Sequelize = require('sequelize')
    , lodash    = require('lodash')
    , sequelize = new Sequelize('sequelize_test', 'root', 'root')
    , db        = {} 

  fs.readdirSync(__dirname)
    .filter(function(file) {
      return (file.indexOf('.') !== 0) && (file !== 'index.js')
    })
    .forEach(function(file) {
      var model = sequelize.import(path.join(__dirname, file))
      db[model.name] = model
    })

  Object.keys(db).forEach(function(modelName) {
    if (db[modelName].options.hasOwnProperty('associate')) {
      db[modelName].options.associate(db)
    }
  })
  // sequelize.sync({force: true})
  module.exports = lodash.extend({
    sequelize: sequelize,
    Sequelize: Sequelize
  }, db)

Coloque el código db anterior en los archivos respectivos en la carpeta db o como quiera llamarlo y luego puede usar su consulta

var db =requerir('./db');

db.order.find({
            where: { id: 0 },
            include: [ db.customer, db.user ]
        })
        .then(function(order){
            console.log(order)
        })