Hi Greg, I've tried to adjust/increase the JVMP heap memory but that does not help solve this problem. I've set the VM option -XX:+HeapDumpOnOutOfMemoryError. No heap dump files are generated, so I assume that is not the problem either. I can isolate this problem within a test case and add a bug report to Drools JIRA. Any other ideas as to how else this could occur, or how to troubleshoot this further? It is really disconcerting. Thanks, Nelson ------------------------------ Message: 3 Date: Tue, 6 Jul 2010 09:05:16 -0700 (PDT) From: Greg Barton <greg_barton(a)yahoo.com&gt; Subject: Re: [rules-users] How is this possible? To: Rules Users List <rules-users(a)lists.jboss.org&gt; Cc: "Richter, Alexander" <ARichter(a)jcvi.org&gt;, &quot;&lt;rules-users(a)lists.jboss.org&gt;&quot; <rules-users(a)lists.jboss.org&gt; Message-ID: <376326.67572.qm(a)web81506.mail.mud.yahoo.com&gt; Content-Type: text/plain; charset="utf-8" Does the amount of heap allocated affect it? I'm wondering if there's a hidden OutOfMemoryError happening. (Which, if you're catching Throwable anywhere, is a possibility. Use the HeapDumpOnOutOfMemoryError VM flag to diagnose this.) And this should be easy to reproduce in your unit tests: just insert many unrelated objects into working memory during the test. In fact you could construct tests thst show the same code succeeding without the excess objects then failing with them. That would be essential if you think this is a core drools problem and want it fixed. GreG