在msdn上的英文解释：
Q: We have a fully patched IIS 5 server and are receiving the following error “Parser Error Message: It is an error to use a section registered allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS.” Can you explain what this means?
A: I love these verbose Asp.net error messages! They often direct you to the solution as well as describe the problem. You’ll see this error when your Asp.net application is configured such that it uses a feature like <authentication mode../> or <sessionState..> that requires an “Application” be defined in the metabase, and that definition is missing. You can correct this by either removing such settings from your web.config files, or by clicking “Create” on the Home Directory, Virtual Directory, or Directory properties tab of a web site, virtual directory, or directory, respectively. This location will require at least the Scripts Only permission and Read permissions as well.
说 像<authentication mode../> or <sessionState..> 这样的东东需要一个Application元数据。 但是你却没有定义。解决方案是：要不你就把你web.config中的这样的东西去掉，要不你就在 Home Directory, Virtual Directory, or Directory properties 那里创建一个对应的web site，虚拟目录和目录。那些东西至少要有Script访问级和Read的权限。