Using JPA with Scala is problematic, as this article describes: http://www.hars.de/2009/03/jpa-with-scala.html

The main obstacle is that Scala 2.7.x does not support nested annotations. This has been fixed in 2.8 trunk several months ago, but 2.8 is still not released.

See also this: http://faler.wordpress.com/2009/08/10/scala-jpa-some-gotchas-to-be-aware...