Utilizando @Transactional no UserDAO

Boa tarde, estou utilizando o spring securtity para autenticação do usuário, porém no meu site eu permito também que o usuário possa se cadastrar na plataforma. Assim, estou utilizando a anottation @Transactional do spring para inserir os dados.

Porém, meu código não funciona quando eu utilizo a anotação @Transactional, como faço então para permitir que um usuário possa se cadastrar na plataforma ?

UserDAO.java

package br.com.utfpr.eventos.dao;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.security.core.userdetails.UserDetailsService;
import org.springframework.security.core.userdetails.UsernameNotFoundException;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;

import br.com.utfpr.eventos.models.User;

@Repository
@Transactional
public class UserDAO implements UserDetailsService {

    @PersistenceContext
    private EntityManager manager;

    public void insert(User user) {
        manager.persist(user);
    }

    public User loadUserByUsername(String email) {

        List<User> users =  manager.createQuery("select u from user u where u.email = :email", User.class)
        .setParameter("email", email)
        .getResultList();

        if(users.isEmpty()) {
            throw new UsernameNotFoundException("Usuário não encontrado");
        }

        return users.get(0);
    }
}

User.java

package br.com.utfpr.eventos.models;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.OneToMany;

import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.userdetails.UserDetails;

@Entity
public class User implements UserDetails {

    private static final long serialVersionUID = 1L;

    @Id
    private String email;
    private String name;
    private String document;
    private String password;

    @OneToMany(fetch=FetchType.EAGER)
    private List<Role> roles = new ArrayList<Role>();

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public String getDocument() {
        return document;
    }
    public void setDocument(String document) {
        this.document = document;
    }

    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public List<Role> getRoles() {
        return roles;
    }
    public void setRoles(List<Role> roles) {
        this.roles = roles;
    }
    public Collection<? extends GrantedAuthority> getAuthorities() {
        return this.roles;
    }
    public String getUsername() {
        return this.email;
    }
    public boolean isAccountNonExpired() {
        return true;
    }
    public boolean isAccountNonLocked() {
        return true;
    }
    public boolean isCredentialsNonExpired() {
        return true;
    }
    public boolean isEnabled() {
        return true;
    }

}

Role.java

package br.com.utfpr.eventos.models;

import javax.persistence.Entity;
import javax.persistence.Id;

import org.springframework.security.core.GrantedAuthority;

@Entity
public class Role implements GrantedAuthority {

    private static final long serialVersionUID = 1L;

    @Id
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAuthority() {
        return this.name;
    }
}

ServletSpringConfiguration.java

package br.com.utfpr.eventos.config;

import javax.servlet.Filter;

import org.springframework.web.filter.CharacterEncodingFilter;
import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

public class ServletSpringMVC extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[] {SecurityConfiguration.class, AppWebConfiguration.class, JPAConfiguration.class};
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class[] {};
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] {"/"};
    }

    @Override
    protected Filter[] getServletFilters() {
        CharacterEncodingFilter encodingFilter = new CharacterEncodingFilter();
        encodingFilter.setForceEncoding(true);
        encodingFilter.setEncoding("UTF-8");

        return new Filter[] {encodingFilter};
    }

}