18장 tag예제 실행시 오류가 나는데 무슨 문제인지 모르겠습니다.

18장 hearder.tag 태그 파일 사용하여 출력하는 예제를 해 보는데요...   다음과 같은 에러가 발생하는데 왜 그런지 ...   <H1 style="FONT-SIZE: 22px; FONT-FAMILY: Tahoma, Arial, sans-serif; FONT-VARIANT: normal; WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: white; FONT-STYLE: normal; LETTER-SPACING: normal; LINE-HEIGHT: normal; BACKGROUND-COLOR: rgb(82,93,118); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">HTTP Status 500 - An exception occurred processing JSP page /use_header.jsp at line 8</H1> <HR style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(82,93,118); FONT: medium Tahoma, Arial, sans-serif; LETTER-SPACING: normal; TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px" SIZE=1 noShade> <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">type Exception report <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">message An exception occurred processing JSP page /use_header.jsp at line 8 <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">description The server encountered an internal error that prevented it from fulfilling this request. <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">exception<PRE style="FONT-VARIANT: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; FONT-WEIGHT: normal; COLOR: rgb(0,0,0); FONT-STYLE: normal; LETTER-SPACING: normal; LINE-HEIGHT: normal; TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">org.apache.jasper.JasperException: An exception occurred processing JSP page /use_header.jsp at line 8 5: <head><title>제목 출력</title></head> 6: <body> 7: 8: <tf:header title="'텍스트 제목'" level="2"/> 9: 10: <tf:header title="${'EL 제목'}" level="3"/> 11: Stacktrace: org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:455) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) </PRE> <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px"> <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">root cause<PRE style="FONT-VARIANT: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; FONT-WEIGHT: normal; COLOR: rgb(0,0,0); FONT-STYLE: normal; LETTER-SPACING: normal; LINE-HEIGHT: normal; TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">javax.servlet.ServletException: javax.servlet.jsp.JspException: java.lang.ClassCastException: org.apache.jasper.el.ELContextImpl cannot be cast to org.apache.jasper.el.ELContextImpl org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:908) org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:841) org.apache.jsp.use_005fheader_jsp._jspService(use_005fheader_jsp.java:101) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) </PRE> <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px"> <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">root cause<PRE style="FONT-VARIANT: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; FONT-WEIGHT: normal; COLOR: rgb(0,0,0); FONT-STYLE: normal; LETTER-SPACING: normal; LINE-HEIGHT: normal; TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">java.lang.ClassCastException: org.apache.jasper.el.ELContextImpl cannot be cast to org.apache.jasper.el.ELContextImpl org.apache.jasper.runtime.PageContextImpl.proprietaryEval‎uate(PageContextImpl.java:1023) org.apache.jsp.tag.webheader_tag.doTag(webheader_tag.java:108) org.apache.jsp.use_005fheader_jsp._jspx_meth_tf_005fheader_005f0(use_005fheader_jsp.java:121) org.apache.jsp.use_005fheader_jsp._jspService(use_005fheader_jsp.java:74) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334) javax.servlet.http.HttpServlet.service(HttpServlet.java:728) </PRE> <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px"> <P style="WHITE-SPACE: normal; TEXT-TRANSFORM: none; WORD-SPACING: 0px; COLOR: rgb(0,0,0); FONT: 12px Tahoma, Arial, sans-serif; LETTER-SPACING: normal; BACKGROUND-COLOR: rgb(255,255,255); TEXT-INDENT: 0px; -webkit-text-stroke-width: 0px">note The full stack trace of the root cause is available in the Apache Tomcat/7.0.39 logs.