Update Entity using EntityManager JPA EclipseLink

I am getting a ERROR: duplicate key value violates unique constraint "users_pkey" Detail: Key (userid)=(2701) already exists. whenever i use the persist model to update my user entity.

In the code sample below: SetLoginAttempts takes in a user entity that has been queried and when i start the transaction i simply set one of the entity's fields and call persist(), then commit the transaction.

/**
* @param user
* @param attemptNumber
*/
@Transactional
public void setLoginAttempts(Users user, int attemptNumber){         
    user.setLoginAttempts(attemptNumber);
    System.out.println(user);
}

Here is how i reference and grab the entity manager:

eFactory = Persistence.createEntityManagerFactory("persistenceUnit");
eManager = eFactory.createEntityManager();

When looking at the stack trace, i noticed that the commit actually injects an insert

Call: INSERT INTO USERS (userID, EMAIL, ISLOCKED, LOGINATTEMPTS, passwordHash, passwordSalt, USERNAME, version) VALUES (?, ?, ?, ?, ?, ?, ?, ?)
bind => [2701, admin@d.com, false, 1, $shiro1$SHA-256$500000$6mqzZ/d/3BLQuJqLh1dDhQ==$NKW7Z++o/JTvf884aDWhP3Uhpyb5fTPMrm4joWnw7nI=, [B@1a8e3115, admin, 1]

What is the proper way to reference an entity manager in Spring roo, update a field and commit the changes?

Edit

I added the @Transactional to the method and the stack trace shows that this is creating the entity manager instance:

2012-03-14 23:49:15,503 ["http-bio-8080"-exec-18] DEBUG org.springframework.orm.jpa.JpaTransactionManager - Creating new transaction with name [org.bixin.dugsi.service.UserService.setLoginAttempts]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT; ''
2012-03-14 23:49:15,503 ["http-bio-8080"-exec-18] DEBUG org.springframework.orm.jpa.JpaTransactionManager - Opened new EntityManager [org.eclipse.persistence.internal.jpa.EntityManagerImpl@46b9979b