For using JPA on scala, you have to use DataNucleus enhancer 1.1.3 or later. But, Google App Engine for Java SDK 1.2.1 containts DataNucleus enhancer 1.1.1. you shoud copy sdk directory other name, and replace lib/tools/orm/datanucleus-enhancer-1.1.1.jar to datanucleus-enhancer-1.1.3.jar. and edit sdk.dir in build.properties to copied sdk directory.