I am getting this error using hibernate 4.3.1 final when i remove (lazy="false") from my xml mapping.
The strange thing is that "lazy" defaults to "false" as said in documentation, so there should be no change.
Or documentation is wrong.

http://docs.jboss.org/hibernate/orm/4.3/manual/en-US/html/ch05.html#mapping-declaration-property#d5e3152