jsp入门问题: 用jbuider9 开发,点run时总是报HTTP Status 500 - Internal Server Error错误??

即使用jbuilder9自带的示例也报这样的错误.
详细错误信息如下:
Apache Tomcat/4.0.6 - HTTP Status 500 - Internal Server Error
type Exception report
message
Internal Server Error
description
The server encountered an internal error (Internal Server Error) that prevented it from fulfilling this request.exception