I'm getting this Hibernate error:

org.hibernate.MappingException: Could not determine type for: 
a.b.c.Results$BusinessDate, for columns: [org.hibernate.mapping.Column(businessDate)]

The class is below. Does anyone know why I'm getting this error??

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "", propOrder = {
    "businessDate"
})
@XmlRootElement(name = "Results")
@Entity(name = "Results")
@Table(name = "RESULT")
@Inheritance(strategy = InheritanceType.JOINED)
@Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
public class Results implements Equals, HashCode
{

    @XmlElement(name = "BusinessDate", required = true)
    protected Results.BusinessDate businessDate;

    public Results.BusinessDate getBusinessDate() {
        return businessDate;
    }

    public void setBusinessDate(Results.BusinessDate value) {
        this.businessDate = value;
    }

    @XmlAccessorType(XmlAccessType.FIELD)
    @XmlType(name = "", propOrder = {
        "raw",
        "display"
    })
    @Entity(name = "Results$BusinessDate")
    @Table(name = "BUSINESSDATE")
    @Inheritance(strategy = InheritanceType.JOINED)
    public static class BusinessDate implements Equals, HashCode
    {

    ....