Could not compile the mapping document

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C#

XML

NHibernate

Hi,
I have a problem with table mapping, I cannot find any error, maybe I have badly written composite-key... Table name and class name is Player_in_Tournament, there is no error...

Error: Could not compile the mapping document: Player_in_Tournament.hbm.xml

Web Form where the Exception is raised:

protected void btnRegister_Click(object sender, EventArgs e)
...
new Insert_Player().Create_Player(tbNickname.Text, tbName.Text, tbSurname.Text, gender, tbEmail.Text);   //here is the error
...

Tournament.hbm.xml:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   namespace="Entities"
                   assembly="Entities">

  <class name="Player_in_Tournament" table="Player_in_Tournament">
    <composite-id>
      <key-property name="Player_ID" column="Player_ID" type="string" />
      <key-property name="Tournament_ID" column="Tournament_ID" type="int" />
    </composite-id>

    <property name="Team_ID"  column="Team_ID" type="int"/>
    <property name="Pozice"  column="Pozice" type="string"/>
  </class>
</hibernate-mapping>

Player_in_Tournament_ID:

public class Player_in_Tournament_ID
    {
        public virtual String Player_ID { get; set; }
        public int Tournament_ID { get; set; }

        public override bool Equals(object obj)
        {
            if (obj == null)
                return false;
            Player_in_Tournament_ID id = (Player_in_Tournament_ID)obj;
            if (id == null)
                return false;
            if (Player_ID == id.Player_ID && Tournament_ID == id.Tournament_ID)
                return true;
            return false;
        }
    }

Player_in_Tournament:

public class Player_in_Tournament
    {
        public virtual Player_in_Tournament_ID Player_in_Tournament_ID { get; set; }
        public virtual int Team_ID { get; set; }
        public virtual String Pozice { get; set; }
    }

Can anyone solve this error?

Thanks!

-Pepin z Hane