欧洲杯扩军16:jsp中出现org.apache.jasper.JasperException

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:358)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)

root cause

java.lang.NullPointerException
org.apache.jsp.bbs1.bbs.checkasp_jsp.htmlz(checkasp_jsp.java:30)
org.apache.jsp.bbs1.bbs.checkasp_jsp.htmln(checkasp_jsp.java:17)
org.apache.jsp.bbs1.bbs.checkasp_jsp._jspService(checkasp_jsp.java:155)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:311)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
javax.servlet.http.HttpServlet.service(HttpServlet.java:856)

note The full stack trace of the root cause is available in the Tomcat logs.

我做的是论坛，普通用户回贴时出现此类问题。
可是管理员回贴就很正常，这个是为什么呢？