A Sig11 is not a good sign. If the code normally runs ok and you occasionally get the Sig11, then most likely you have some sort of hardware fault - like bad memory, etc. However, if it is fairly repeatable, then the issue is probably the JVM. First try obtaining a different JDK/JVM. Otherwise if that doesn't shake the problem you might start suspecting something like faulty memory or other hardware.
Thanks for your help jonlee.