项目没有bug，隔了一个月再打开项目很多jsp页面爆500异常，似与jstl有关，希望大神们指点一二

org.apache.jasper.JasperException: /admin/SystemLog/index.jsp(81,3) The function size must be used with a prefix when a default namespace is not specified
org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:40)
org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:407)
org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:148)
org.apache.jasper.compiler.Validator$ValidateVisitor$1FVVisitor.visit(Validator.java:1528)
org.apache.jasper.compiler.ELNode$Function.accept(ELNode.java:131)
org.apache.jasper.compiler.ELNode$Nodes.visit(ELNode.java:206)
org.apache.jasper.compiler.ELNode$Visitor.visit(ELNode.java:248)
org.apache.jasper.compiler.ELNode$Root.accept(ELNode.java:56)
org.apache.jasper.compiler.ELNode$Nodes.visit(ELNode.java:206)
org.apache.jasper.compiler.Validator$ValidateVisitor.validateFunctions(Validator.java:1553)
org.apache.jasper.compiler.Validator$ValidateVisitor.getJspAttribute(Validator.java:1326)
org.apache.jasper.compiler.Validator$ValidateVisitor.checkXmlAttributes(Validator.java:1176)
org.apache.jasper.compiler.Validator$ValidateVisitor.visit(Validator.java:840)
org.apache.jasper.compiler.Node$CustomTag.accept(Node.java:1530)
org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2361)
org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2411)
org.apache.jasper.compiler.Validator$ValidateVisitor.visit(Validator.java:859)
org.apache.jasper.compiler.Node$CustomTag.accept(Node.java:1530)
org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2361)
org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2411)
org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2417)
org.apache.jasper.compiler.Node$Root.accept(Node.java:495)
org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2361)
org.apache.jasper.compiler.Validator.validateExDirectives(Validator.java:1785)
org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:198)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:354)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:334)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:321)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:592)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
com.ysdit.xiaomi.servlet.SystemlogIndexServlet.doGet(SystemlogIndexServlet.java:27)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.45 logs.

Apache Tomcat/6.0.45

对项目clean再build失效。

？？？怎么操作？clean是什么鬼？

要么class文件丢失 要么jar包丢失

index.jsp的第81行，是什么贴出来看看

如果使用eclipse的话（我的是日文环境，如果是中文环境的话，根据相应的位置操作即可）