Nhibernate报错集合类型转换错误！

[dh1314al]

这我的实体类映射文件

    <?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="MyBookShop.Model.Book, MyBookShop.Model" table="Books">
    <id name="Id" type="Int32" unsaved-value="null">
      <column name="Id" length="4" sql-type="int" not-null="true" unique="true" index="PK_Book"/>
      <generator class="native" />
    </id>
    <property name="Title" type="String">
      <column name="Title" length="200" sql-type="nvarchar" not-null="true"/>
    </property>
    <property name="Author" type="String">
      <column name="Author" length="200" sql-type="nvarchar" not-null="true"/>
    </property>
    <property name="PublishDate" type="DateTime">
      <column name="PublishDate" length="8" sql-type="datetime" not-null="true"/>
    </property>
    <property name="ISBN" type="String">
      <column name="ISBN" length="50" sql-type="nvarchar" not-null="true" unique="true" index="IX_Books_ISBN"/>
    </property>
    <property name="WordsCount" type="Int32">
      <column name="WordsCount" length="4" sql-type="int" not-null="true"/>
    </property>
    <property name="UnitPrice" type="Decimal">
      <column name="UnitPrice" length="8" sql-type="money" not-null="true"/>
    </property>
    <property name="ContentDescription" type="String">
      <column name="ContentDescription" sql-type="nvarchar" not-null="false"/>
    </property>
    <property name="AurhorDescription" type="String">
      <column name="AurhorDescription" sql-type="nvarchar" not-null="false"/>
    </property>
    <property name="EditorComment" type="String">
      <column name="EditorComment" sql-type="nvarchar" not-null="false"/>
    </property>
    <property name="TOC" type="String">
      <column name="TOC" sql-type="nvarchar" not-null="false"/>
    </property>
    <property name="Clicks" type="Int32">
      <column name="Clicks" length="4" sql-type="int" not-null="true"/>
    </property>
    <many-to-one name="Category" class="MyBookShop.Model.Category, MyBookShop.Model" foreign-key="FK_Book_Category">
      <column name="CategoryId" length="4" sql-type="int" not-null="true"/>
    </many-to-one>
    <many-to-one name="Publisher" class="MyBookShop.Model.Publisher, MyBookShop.Model" foreign-key="FK_Books_Publishers">
      <column name="PublisherId" length="4" sql-type="int" not-null="true"/>
    </many-to-one>
    <bag name="BookReaderCommentses" inverse="true" lazy="true" cascade="all-delete-orphan">
      <key column="BookId"/>
      <one-to-many class="MyBookShop.Model.ReaderComment, MyBookShop.Model"/>
    </bag>
  </class>
</hibernate-mapping>

这我的实体类

using System;
using System.Collections.Generic;
using System.Text;

namespace MyBookShop.Model
{
    [Serializable()]
    public class Book
    {
        #region 字段
        private int id;
        private string title;
        private string author;
        private Publisher publisher;
        private DateTime publishDate;
        private string iSBN;
        private int wordsCount;
        private int unitPrice;
        private string contentDescription;
        private string aurhorDescription;
        private string editorComment;
        private string tOC;
        private Category category;
        private int clicks;
        private List<ReaderComment> bookReaderCommentses = null;
        #endregion
        #region 属性

        public virtual List<ReaderComment> BookReaderCommentses
        {
            get { return bookReaderCommentses; }
            set { bookReaderCommentses = value; }
        }
        public virtual string ContentDescription
        {
            get { return contentDescription; }
            set { contentDescription = value; }
        }
        public virtual DateTime PublishDate
        {
            get { return publishDate; }
            set { publishDate = value; }
        }
        public virtual int Clicks
        {
            get { return clicks; }
            set { clicks = value; }
        }

        public virtual Category Category
        {
            get { return category; }
            set { category = value; }
        }

        public virtual string TOC
        {
            get { return tOC; }
            set { tOC = value; }
        }
        public virtual string EditorComment
        {
            get { return editorComment; }
            set { editorComment = value; }
        }
        public virtual string AurhorDescription
        {
            get { return aurhorDescription; }
            set { aurhorDescription = value; }
        }
        public virtual int UnitPrice
        {
            get { return unitPrice; }
            set { unitPrice = value; }
        }

        public virtual int WordsCount
        {
            get { return wordsCount; }
            set { wordsCount = value; }
        }

        public virtual string ISBN
        {
            get { return iSBN; }
            set { iSBN = value; }
        }

        public virtual Publisher Publisher
        {
            get { return publisher; }
            set { publisher = value; }
        }

        public virtual string Author
        {
            get { return author; }
            set { author = value; }
        }

        public virtual string Title
        {
            get { return title; }
            set { title = value; }
        }

        public virtual int Id
        {
            get { return id; }
            set { id = value; }
        }
        #endregion
    }
}

报错信息:注:不是配置的问题,我执行增、删、改、查都可以唯独查的类中包含集合的时候就报转换无效！我知道什么原因请给位指教！报错信息不完整的话 加QQ：498795832 详聊 在线等！！！！非常急
Message:Invalid Cast (check your mapping for property type mismatches); setter of MyBookShop.Model.Book
InnerException:{"指定的转换无效。"}
StackTrace: 在 (Object , Object[] , SetterCallback )
在 NHibernate.Bytecode.Lightweight.AccessOptimizer.SetPropertyValues(Object target, Object[] values)
在 NHibernate.Tuple.Entity.PocoEntityTuplizer.SetPropertyValuesWithOptimizer(Object entity, Object[] values)

[dh1314al]

怎么没高手指教了????