This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
This discussion is old and you've probably fixed your problems and are happy with the (fantastic imho) Play framework or moved on to another.
The error is caused by the fact that you try to extend play.jpa.Model which normally is a good plan but it assumes you let Play generate a Long as your id automatically. In this case you're using an Integer as id which you manage yourself. Play supports this without any problem but you have to extend the GenericModel super class instead of Model. That will (or would have) fixed your problems.