How to get rid of 'java.lang.IllegalArgumentException: Unknown entity' while running a simple hibernate app?

I am new to Hibernate. While creating a small app using it I got following exception:

Exception in thread "main" java.lang.IllegalArgumentException: Unknown entity:
model.Students at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:223) at controller.Main.main(Main.java:50)

Can anybody please help me out?

The Entity classes are as follows:

Other details:
NetBeans Version: 6.7.1  
Hibernate : 3.2.5

Entity Students

package model;  
import java.io.Serializable;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;

@Entity
public class Students implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String name;

    @OneToOne(cascade=CascadeType.ALL)
    private Address address;

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public String getName() {
        return name;
    }

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


    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }
}

Another Entity Class

package model;

import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;  
@Entity

public class Address implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)