JPQL Query a list of Strings inside an Entity

I'm using Java EE7 with a GlassFish 4.1 Server to build a system where basically you can post Ideas, and each Idea may have tags. I've declared the entity Idea as:

@Entity
@Table(name = "IDEAS")
public class Idea implements Serializable {

// Id, description, etc.

@ElementCollection
private List<String> tags;

// Getters, Setter, etc.
}

After reading JPA: Query an embeddable List inside an entity I tried to find by Tag the following way:

public List<Idea> getIdeasWithTag(String tag) {
    String queryStr = "select ideatags from Idea i "
            + "inner join i.tags ideatags "
            + "where ideatags.tags = :pTag";
    Object res = em.createQuery(queryStr)
            .setParameter("pTag", tag)
            .getResultList();
    return (List<Idea>) res;
}

But I'm getting a TransactionRolledbackLocalException caused by:

Caused by: java.lang.IllegalArgumentException: An exception occurred while creating a query in EntityManager: Exception Description: Problem compiling [select ideatags from Idea i inner join i.tags ideatags where ideatags.tags = :pTag]. [61, 74] The state field path 'ideatags.tags' cannot be resolved to a valid type.

I appreciate any help, thanks in advance!!