JPA: java.lang.IllegalArgumentException: Removing a detached

One of the common issues that I end up debugging is the following exception:

java.lang.IllegalArgumentException: Removing a detached instance

When does this occur?: While removing a record.
Why does this occur?: You are trying to delete a record which is retrieved in another transaction (probably even trying to delete a record that is stored in user HTTP session).
How to fix it?: Make sure you retrieve the record in the same transaction. Sample code for the same:

   public void removeOrganization(Organization org) {
       if (org.getId() != null) {
           org=em.find(Organization.class, org.getId());
           em.remove(org);     
       } else {
          // your error logic.
       }
   }