Struts Link causes NP

I'm working with Struts 1 The following lines in my welcome jsp are working with AS 5.0 fine (showing a help jsp page):

<html:link href="javascript:popUp('/diaryinfo/welcome.jspa?method=showWelcomeHelp')">
<html:img page="/images/b_info_gruen.gif" alt="info" border="0"/></html:link>

Now I want to change to AS 6.0.0, but I get the following exception after calling the start welcome page. Without this link the welcome page is shown:

18:37:26,562 INFO [com.mediit.diaryinfo.web.filter.SignOnFilter] ...uri=welcome.jspa
18:37:26,578 INFO [com.mediit.diaryinfo.web.action.WelcomeAction] welcome()
18:37:26,625 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[localhost].[/diaryinfo].[jsp]] Servlet.service() for servlet jsp threw exception: java.lang.NullPointerException
at org.apache.jasper.compiler.Parser.parseBody(Parser.java:1598) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseOptionalBody(Parser.java:976) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseCustomTag(Parser.java:1247) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseElements(Parser.java:1421) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseBody(Parser.java:1633) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseOptionalBody(Parser.java:976) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseCustomTag(Parser.java:1247) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseElements(Parser.java:1421) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parse(Parser.java:130) [:6.0.0.Final]
at org.apache.jasper.compiler.ParserController.doParse(ParserController.java:255) [:6.0.0.Final]
at org.apache.jasper.compiler.ParserController.parse(ParserController.java:103) [:6.0.0.Final]
at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:196) [:6.0.0.Final]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:358) [:6.0.0.Final]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:338) [:6.0.0.Final]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:325) [:6.0.0.Final]
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:607) [:6.0.0.Final]
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:312) [:6.0.0.Final]
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:326) [:6.0.0.Final]
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:253) [:6.0.0.Final]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [:1.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:324) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:734) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:541) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:479) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:407) [:6.0.0.Final]
at org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1085) [:1.2.9]
at org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:398) [:1.2.9]
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:241) [:1.2.9]
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196) [:1.2.9]
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414) [:1.2.9]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:734) [:1.0.0.Final]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [:1.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:324) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.0.0.Final]
at com.mediit.diaryinfo.web.filter.SignOnFilter.doFilter(SignOnFilter.java:156) [:]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:274) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.0.0.Final]
at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(Unknown Source) [:]
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(Unknown Source) [:]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:274) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.0.0.Final]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [:6.0.0.Final]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) [:6.0.0.Final]
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:181) [:6.0.0.Final]
at org.jboss.modcluster.catalina.CatalinaContext$RequestListenerValve.event(CatalinaContext.java:285) [:1.1.0.Final]
at org.jboss.modcluster.catalina.CatalinaContext$RequestListenerValve.invoke(CatalinaContext.java:261) [:1.1.0.Final]
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:88) [:6.0.0.Final]
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:100) [:6.0.0.Final]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) [:6.0.0.Final]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [:6.0.0.Final]
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158) [:6.0.0.Final]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [:6.0.0.Final]
at org.jboss.web.tomcat.service.request.ActiveRequestResponseCacheValve.invoke(ActiveRequestResponseCacheValve.java:53) [:6.0.0.Final]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:362) [:6.0.0.Final]
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [:6.0.0.Final]
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:654) [:6.0.0.Final]
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:951) [:6.0.0.Final]
at java.lang.Thread.run(Thread.java:619) [:1.6.0_05]

18:37:26,687 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[localhost].[/diaryinfo].[action]] Servlet.service() for servlet action threw exception: java.lang.NullPointerException
at org.apache.jasper.compiler.Parser.parseBody(Parser.java:1598) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseOptionalBody(Parser.java:976) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseCustomTag(Parser.java:1247) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseElements(Parser.java:1421) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseBody(Parser.java:1633) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseOptionalBody(Parser.java:976) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseCustomTag(Parser.java:1247) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parseElements(Parser.java:1421) [:6.0.0.Final]
at org.apache.jasper.compiler.Parser.parse(Parser.java:130) [:6.0.0.Final]
at org.apache.jasper.compiler.ParserController.doParse(ParserController.java:255) [:6.0.0.Final]
at org.apache.jasper.compiler.ParserController.parse(ParserController.java:103) [:6.0.0.Final]
at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:196) [:6.0.0.Final]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:358) [:6.0.0.Final]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:338) [:6.0.0.Final]
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:325) [:6.0.0.Final]
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:607) [:6.0.0.Final]
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:312) [:6.0.0.Final]
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:326) [:6.0.0.Final]
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:253) [:6.0.0.Final]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [:1.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:324) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:734) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:541) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:479) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:407) [:6.0.0.Final]
at org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1085) [:1.2.9]
at org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:398) [:1.2.9]
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:241) [:1.2.9]
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196) [:1.2.9]
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414) [:1.2.9]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:734) [:1.0.0.Final]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [:1.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:324) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.0.0.Final]
at com.mediit.diaryinfo.web.filter.SignOnFilter.doFilter(SignOnFilter.java:156) [:]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:274) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.0.0.Final]
at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(Unknown Source) [:]
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(Unknown Source) [:]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:274) [:6.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.0.0.Final]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [:6.0.0.Final]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) [:6.0.0.Final]
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:181) [:6.0.0.Final]
at org.jboss.modcluster.catalina.CatalinaContext$RequestListenerValve.event(CatalinaContext.java:285) [:1.1.0.Final]
at org.jboss.modcluster.catalina.CatalinaContext$RequestListenerValve.invoke(CatalinaContext.java:261) [:1.1.0.Final]
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:88) [:6.0.0.Final]
at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:100) [:6.0.0.Final]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) [:6.0.0.Final]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [:6.0.0.Final]
at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158) [:6.0.0.Final]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [:6.0.0.Final]
at org.jboss.web.tomcat.service.request.ActiveRequestResponseCacheValve.invoke(ActiveRequestResponseCacheValve.java:53) [:6.0.0.Final]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:362) [:6.0.0.Final]
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [:6.0.0.Final]
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:654) [:6.0.0.Final]
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:951) [:6.0.0.Final]
at java.lang.Thread.run(Thread.java:619) [:1.6.0_05]