The JPA Hibernate cannot work with variables annotated with the annotation @ElementCollection. When this annotation is used and for example the annotation @ManyToOne is used as well, the JBDS shows errors at places where they shouldn't be.
Follow my instructions to reproduce this issue:
1. Download attached reproducer ui-ejb-minimized.zip
2. Extract it
3. Import the project into JBDS as an existing maven project
4. Look at the errors. There are two errors for this project:

Target entity is not defined	Person.java	/ui-ejb-minimized/src/main/java/org/jboss/seam/example/ui	line 25	JPA Problem
The given name of the entity "org.jboss.seam.example.ui.Country" is empty	Country.java	/ui-ejb-minimized/src/main/java/org/jboss/seam/example/ui	line 9	JPA Problem

Both of them are unnecessary because both the target entity and the name of the entity are optional.
5. Comment the variable:

@ElementCollection
private List<String> notes = new ArrayList<String>();

6. Save the class Person
7. Click on Project -> Clean
Then all the errors will disappear.
8. uncomment the variable with the annotation back
9. Save the class Person
10. Click on Project -> Clean
The two errors are back

The attached reproducer is minimized Seam project ui-ejb of the example ui. https://github.com/seam2/jboss-seam/tree/Seam_2_3/examples/ui
This Seam example is more complicated and the number of the wrong errors shown in JBDS is much bigger.