I upgraded to Jenkins 1.491 a few days okay and performed a couple of builds.
Today all nodes show all build executors as "Dead!" which I have never seen before. They refuse to come back even after restarting Jenkins.

The assert (out of bounds exception) is the same for all threads.
Jenkins is now completely unusable.
I tried upgrading to 1.492 just released hoping it might be a fix
but to no avail.

Thread has died

java.lang.ArrayIndexOutOfBoundsException: Assertion error: failing to load #7025 EXACT: lo=9,hi=5,size=19,size2=19
at jenkins.model.lazy.AbstractLazyLoadRunMap.search(AbstractLazyLoadRunMap.java:418)
at jenkins.model.lazy.AbstractLazyLoadRunMap.getByNumber(AbstractLazyLoadRunMap.java:502)
at jenkins.model.lazy.AbstractLazyLoadRunMap.search(AbstractLazyLoadRunMap.java:355)
at hudson.model.AbstractBuild.getPreviousBuild(AbstractBuild.java:207)
at hudson.model.AbstractBuild.getPreviousBuild(AbstractBuild.java:100)
at hudson.model.Job.getLastBuildsOverThreshold(Job.java:856)
at hudson.model.Job.getEstimatedDuration(Job.java:863)
at hudson.model.queue.MappingWorksheet.<init>(MappingWorksheet.java:320)
at hudson.model.queue.MappingWorksheet.<init>(MappingWorksheet.java:303)
at hudson.model.Queue.maintain(Queue.java:1033)
at hudson.model.Queue.pop(Queue.java:861)
at hudson.model.Executor.grabJob(Executor.java:284)
at hudson.model.Executor.run(Executor.java:205)

Log:

Caused by: java.lang.ArrayIndexOutOfBoundsException: Assertion error: failing to load #3090 EXACT: lo=1,hi=0,size=1,size2=1
at jenkins.model.lazy.AbstractLazyLoadRunMap.search(AbstractLazyLoadRunMap.java:418)
at jenkins.model.lazy.AbstractLazyLoadRunMap.getByNumber(AbstractLazyLoadRunMap.java:502)
at jenkins.model.lazy.AbstractLazyLoadRunMap.search(AbstractLazyLoadRunMap.java:355)
at hudson.model.AbstractBuild.getPreviousBuild(AbstractBuild.java:207)
at hudson.model.AbstractBuild.getPreviousBuild(AbstractBuild.java:100)
at hudson.model.Job.getLastFailedBuild(Job.java:824)
... 135 more

Nov 28, 2012 3:02:51 PM jenkins.model.lazy.AbstractLazyLoadRunMap search
WARNING: Assertion error: failing to load #3090 EXACT: lo=1,hi=0,size=1,size2=1
java.lang.Exception
at jenkins.model.lazy.AbstractLazyLoadRunMap.search(AbstractLazyLoadRunMap.java:417)
at jenkins.model.lazy.AbstractLazyLoadRunMap.getByNumber(AbstractLazyLoadRunMap.java:502)
at jenkins.model.lazy.AbstractLazyLoadRunMap.search(AbstractLazyLoadRunMap.java:355)
at hudson.model.AbstractBuild.getPreviousBuild(AbstractBuild.java:207)
at hudson.model.AbstractBuild.getPreviousBuild(AbstractBuild.java:100)
at hudson.model.Job.getLastFailedBuild(Job.java:824)
at sun.reflect.GeneratedMethodAccessor92.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:616)
at org.apache.commons.jexl.util.PropertyExecutor.execute(PropertyExecutor.java:125)
at org.apache.commons.jexl.util.introspection.UberspectImpl$VelGetterImpl.invoke(UberspectImpl.java:314)
at org.apache.commons.jexl.parser.ASTArrayAccess.evaluateExpr(ASTArrayAccess.java:185)
at org.apache.commons.jexl.parser.ASTIdentifier.execute(ASTIdentifier.java:75)
at org.apache.commons.jexl.parser.ASTReference.execute(ASTReference.java:83)
at org.apache.commons.jexl.parser.ASTReference.value(ASTReference.java:57)
at org.apache.commons.jexl.parser.ASTReferenceExpression.value(ASTReferenceExpression.java:51)
at org.apache.commons.jexl.ExpressionImpl.evaluate(ExpressionImpl.java:80)
at hudson.ExpressionFactory2$JexlExpression.evaluate(ExpressionFactory2.java:72)
at org.apache.commons.jelly.tags.core.CoreTagLibrary$3.run(CoreTagLibrary.java:134)
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.JellyViewScript.run(JellyViewScript.java:81)
at org.kohsuke.stapler.jelly.IncludeTag.doTag(IncludeTag.java:146)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:161)
at org.apache.commons.jelly.tags.core.ForEachTag.doTag(ForEachTag.java:150)
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.tags.core.CoreTagLibrary$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:119)
at org.apache.commons.jelly.TagSupport.invokeBody(TagSupport.java:161)
at org.apache.commons.jelly.tags.core.ForEachTag.doTag(ForEachTag.java:150)
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.apache.commons.jelly.tags.core.CoreTagLibrary$1.run(CoreTagLibrary.java:98)
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$2.run(CoreTagLibrary.java:105)
at org.kohsuke.stapler.jelly.CallTagLibScript.run(CallTagLibScript.java:119)
at org.kohsuke.stapler.jelly.groovy.JellyBuilder.doInvokeMethod(JellyBuilder.java:283)
at org.kohsuke.stapler.jelly.groovy.Namespace$ProxyImpl.invoke(Namespace.java:92)
at $Proxy32.projectView(Unknown Source)
at lib.JenkinsTagLib$projectView.call(Unknown Source)
at hudson.model.View.main.run(main.groovy:14)
at org.kohsuke.stapler.jelly.groovy.GroovierJellyScript.run(GroovierJellyScript.java:66)
at org.kohsuke.stapler.jelly.groovy.GroovierJellyScript.run(GroovierJellyScript.java:59)
at org.kohsuke.stapler.jelly.IncludeTag.doTag(IncludeTag.java:146)
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:98)
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.apache.commons.jelly.tags.core.CoreTagLibrary$1.run(CoreTagLibrary.java:98)
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:119)
at org.apache.commons.jelly.impl.ScriptBlock.run(ScriptBlock.java:95)
at org.kohsuke.stapler.jelly.CallTagLibScript$1.run(CallTagLibScript.java:98)
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.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.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:119)
at org.kohsuke.stapler.jelly.CompressTag.doTag(CompressTag.java:44)
at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:269)
at org.kohsuke.stapler.jelly.JellyViewScript.run(JellyViewScript.java:81)
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:107)
at org.kohsuke.stapler.jelly.JellyFacet.handleIndexRequest(JellyFacet.java:127)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:562)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:658)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:624)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:658)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:487)
at org.kohsuke.stapler.Stapler.service(Stapler.java:164)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:45)
at winstone.ServletConfiguration.execute(ServletConfiguration.java:248)
at winstone.RequestDispatcher.forward(RequestDispatcher.java:333)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:376)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:95)
at hudson.plugins.audit_trail.AuditTrailFilter.doFilter(AuditTrailFilter.java:66)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:98)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:87)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:47)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
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 org.acegisecurity.ui.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:166)
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 org.acegisecurity.ui.basicauth.BasicProcessingFilter.doFilter(BasicProcessingFilter.java:173)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.ApiTokenFilter.doFilter(ApiTokenFilter.java:63)
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:66)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:164)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:50)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:81)
at winstone.FilterConfiguration.execute(FilterConfiguration.java:194)
at winstone.RequestDispatcher.doFilter(RequestDispatcher.java:366)
at winstone.RequestDispatcher.forward(RequestDispatcher.java:331)
at winstone.RequestHandlerThread.processRequest(RequestHandlerThread.java:215)
at winstone.RequestHandlerThread.run(RequestHandlerThread.java:138)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:679)

Trivial by comparison but the message on the more details page is out of date (referring to Hudson):

"Hudson dedicates a java.lang.Thread for each executor. Under normal operation, this thread is alive all the time (although unless a build is going on the thread is sleeping.) The "dead executor" sign (see the picture on the right) happens when this thread dies unexpectedly. When this happens, please check your Hudson system log (http://server/hudson/log) and look for a stack trace, then report that to Hudson users list or the issue tracker."