nhibernate spi初始化错误

我刚刚开始使用NHibernate，我正在使用《快速入门指南》，但我不断地遇到这个错误。我做的每件事都完全按照《快速入门指南》的要求去做，每次都会遇到这个错误

<error>
{"The type initializer for 'NHibernate.Cfg.Configuration' threw an exception."}
</error>

内部例外情况是：

<Inner Exception>
{"The type initializer for 'log4net.spi.LoggerManager' threw an exception."}
</Inner Exception>

{“log4net.spi.LoggerManager”的类型初始值设定项引发了异常。”}

以及内部异常的堆栈跟踪：

<Stack Trace>
"   at log4net.spi.LoggerManager.GetLogger(Assembly domainAssembly, String name)\r\n        at log4net.LogManager.GetLogger(Assembly domainAssembly, String name)\r\n   at    log4net.LogManager.GetLogger(Type type)\r\n   at NHibernate.Cfg.Configuration..cctor()"
</Stack Trace>

“在log4net.spi.LoggerManager.GetLogger（Assembly domainAssembly，String name）\r\n在log4net.LogManager.GetLogger（Assembly domainAssembly，String name）\r\n在log4net.LogManager.GetLogger（Type Type）\r\n在NHibernate.Cfg.Configuration..cctor（）”

“这看起来像是log4net异常。log4net也不应该在其程序集之外抛出任何异常。”

<Stack Trace>
"   at log4net.spi.LoggerManager.GetLogger(Assembly domainAssembly, String name)\r\n        at log4net.LogManager.GetLogger(Assembly domainAssembly, String name)\r\n   at    log4net.LogManager.GetLogger(Type type)\r\n   at NHibernate.Cfg.Configuration..cctor()"
</Stack Trace>