I'm having an exception all the time when trying to add a new entity :
All fields are filled in, only ID is missing.
I'm adding an image :
For solving this problem it is necessary to change the type of the entity. Open the Entity Object, go to attributes tab, select ID field and in property inspector tab change Type NUMBER to DBSequence.
In the case that you have an ID of type BigDecimal, it's necessary to double click the attribute to make appear "Edit Attribute" Popup, then in browse for the Type label, and search oracle.jpo.doman.DBSequence, then do OK.