After downgrade to URL Trigger plugin 0.37 and a reload of Jenkins it seems to be working again.

It turns out that it wasn't the downgrade to URL Trigger plugin 0.37 that made it work. It was the restart of Jenkins. I got the same problem with URL Trigger plugin 0.37 efter fiddling with enable/disable of the jobs (can't reproduce it right now, but will try some more).

Increasing priority because of this.

Tried the following combinations without luck:

Jenkins ver. 1.626 + Jenkins URL Trigger plugin 0.37
Jenkins ver. 1.626 + Jenkins URL Trigger plugin 0.40
Jenkins ver. 1.628 + Jenkins URL Trigger plugin 0.37
Jenkins ver. 1.628 + Jenkins URL Trigger plugin 0.40

A restart seems to always resolve it (reload is not enough).

Looks lie I have hit similar:

javax.servlet.ServletException: org.apache.commons.jelly.JellyTagException: jar:file:/var/lib/jenkins/plugins/urltrigger/WEB-INF/lib/urltrigger.jar!/org/jenkinsci/plugins/urltrigger/URLTriggerAction/index.jelly:28:62: <st:include> No page found 'sidepanel.jelly' for class org.jenkinsci.plugins.urltrigger.URLTrigger$InternalURLTriggerAction
at org.kohsuke.stapler.jelly.JellyClassTearOff.serveIndexJelly(JellyClassTearOff.java:117)
at org.kohsuke.stapler.jelly.JellyFacet.handleIndexRequest(JellyFacet.java:127)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:735)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.MetaClass$13.dispatch(MetaClass.java:411)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:249)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.MetaClass$6.doDispatch(MetaClass.java:249)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:53)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:649)
at org.kohsuke.stapler.Stapler.service(Stapler.java:238)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:686)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1494)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:132)
at com.smartcodeltd.jenkinsci.plugin.assetbundler.filters.LessCSS.doFilter(LessCSS.java:46)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:129)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:123)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:49)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:117)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.BasicHeaderProcessor.doFilter(BasicHeaderProcessor.java:93)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:67)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:171)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1482)
at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1474)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:499)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:533)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:428)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
at org.eclipse.jetty.server.Server.handle(Server.java:370)
at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:489)
at org.eclipse.jetty.server.AbstractHttpConnection.headerComplete(AbstractHttpConnection.java:949)
at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.headerComplete(AbstractHttpConnection.java:1011)
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:644)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:668)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
at winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.commons.jelly.JellyTagException: jar:file:/var/lib/jenkins/plugins/urltrigger/WEB-INF/lib/urltrigger.jar!/org/jenkinsci/plugins/urltrigger/URLTriggerAction/index.jelly:28:62: <st:include> No page found 'sidepanel.jelly' for class org.jenkinsci.plugins.urltrigger.URLTrigger$InternalURLTriggerAction
at org.kohsuke.stapler.jelly.IncludeTag.doTag(IncludeTag.java:124)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.CallTagLibScript$1.run(CallTagLibScript.java:99)
at org.apache.commons.jelly.tags.define.InvokeBodyTag.doTag(InvokeBodyTag.java:91)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.ReallyStaticTagLibrary$1.run(ReallyStaticTagLibrary.java:99)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:120)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.JellyViewScript.run(JellyViewScript.java:95)
at org.kohsuke.stapler.jelly.DefaultScriptInvoker.invokeScript(DefaultScriptInvoker.java:63)
at org.kohsuke.stapler.jelly.DefaultScriptInvoker.invokeScript(DefaultScriptInvoker.java:53)
at org.kohsuke.stapler.jelly.JellyClassTearOff.serveIndexJelly(JellyClassTearOff.java:112)

@Lance Zimmerman: please vote and maybe we can get this fixed.

magjac I shows I did vote but I removed and added back again.

Lance Zimmerman There was (and is) only one vote and I couldn't (can't) vote, so I guessed it must be mine, but perhaps I can't vote because I am the reporter? Sorry for the confusion.

Gregory Boissinot Any plans on fixing this issue or suggestions for workaorund?

danielbeck: You usually can spot what's wrong quickly. Can you help here? This problem is currently blocking our whole CI pipeline. Restart of Jenkins doesn't always help. Also periodic triggering seems to suffer from this.

The jenkins log is filled with messages like this, almost 50 every minute (when seconds are == 00):

nov 16, 2015 8:00:00 FM org.jenkinsci.lib.xtrigger.AbstractTrigger run
SEVERE: Severe error during the trigger execution null
java.lang.NullPointerException
at org.jenkinsci.plugins.urltrigger.URLTrigger.getLogFile(URLTrigger.java:399)
at org.jenkinsci.lib.xtrigger.AbstractTrigger.run(AbstractTrigger.java:132)
at hudson.triggers.Trigger.checkTriggers(Trigger.java:282)
at hudson.triggers.Trigger$Cron.doRun(Trigger.java:221)
at hudson.triggers.SafeTimerTask.run(SafeTimerTask.java:51)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)

The trigger has a null job. Could be related to an optimization that was in core between 1.621 and 1.634 before getting reverted. Does this issue occur with current LTS or main line releases?

Tanks Daniel for your quick response.

I was running 1.628 until this morning when I upgraded to 1.638. I haven't seen the problem since, but I think it's to soon to say it's gone, because I don't know what I have done before that triggered the problem. I haven't tried the LTS (wasn't even aware that it existed).

Keeping my finger crossed though.

Both Jenkins and URLTriggerPlugin have moved on considerably since this issue was reported.  Could not reproduce and assuming no longer an issue