The following types may not be used as proxies

异常：

The following types may not be used as proxies:
NHibernateDemo.DataAccess.DomainObjects.Customer: method get_Name should be virtual
NHibernateDemo.DataAccess.DomainObjects.PurchaseItem: method set_Id should be virtual.....

需要改的有两点：
例如：Customer.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns=" urn:nhibernate-mapping-2.2">
<class name="NHibernateDemo.DataAccess.DomainObjects.Customer, NHibernateDemo.DataAccess" table="Customer"lazy="false">
<id name="Id" type="Int32" unsaved-value="null">
<column name="ID" length="4" sql-type="int" not-null="true" unique="true" />
<generator class="native" />
</id>
<property name="Name" type="String">
<column name="Name" length="30" sql-type="nvarchar" not-null="true"/>
</property>
<bag name="CustomerPurchases" inverse="true" lazy="true" cascade="all-delete-orphan">
<key column="CustomerID"/>
<one-to-many class="NHibernateDemo.DataAccess.DomainObjects.Purchase, NHibernateDemo.DataAccess"/>
</bag>
</class>
</hibernate-mapping>

1.未能找到元素“urn:nhibernate-mapping-2.0:hibernate-mapping”的架构信息
把 原来的urn:nhibernate-mapping-2.0改为urn:nhibernate-mapping-2.2

2 .在class中添加lazy=false.

在网上查的资料有三种解决方案，下面转载
1.   You can follow the advice of the exception and add "virtual" to all of your properties, and make sure your class is non-sealed.Obviously you'll want to do this if you think you might want to take advantage of the lazy-initializing proxy feature.   However, changing your classes may notbe practical or advisable if you have a legacy codebase, or it may just bother you that a "transparent" persistence framework is dictating how you design certain aspects of your value classes.   That's where Options 2 and 3 come in.   Both of those involve changing back to the old behavior.

          2.  To change the lazy-initialization proxy setting for a specific class, you can add a "lazy='false'" attribute to the <class> mapping element.   This might look something like:

<class
name="NorthwindClasses.Category, NorthwindClasses"
table="Categories"
   lazy="false"
>

        3.  To change the lazy-initialization proxy setting for all classes in a given mapping file, you can add a "default-lazy='false'" attribute to the <hibernate-mapping> element, as follows:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"default-lazy="false">

Unfortunately, Option 3 doesn't really help you much if you do one <class> mapping per <hibernate-mapping> file, a practice which I personally follow and recommend.   It's too bad, but there doesn't seem to be any way to set this default in the <nhibernate> global configuration.   But if you do happen to have all of your <class>'s in one .hbm.xml file, "default-lazy" can help you out.