I am running some custom jmx beans inside a jboss-4.2 running on jdk1.5. With load time weaving enabled, I get to see the following exception:

java.util.ConcurrentModificationException
 at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(LinkedHashMap.java:365)
 at java.util.LinkedHashMap$ValueIterator.next(LinkedHashMap.java:380)
 at org.jboss.aop.instrument.JoinpointSimpleClassifier.classifyJoinpoint(JoinpointSimpleClassifier.java:63)
 at org.jboss.aop.instrument.JoinpointClassifier.classifyMethodExecution(JoinpointClassifier.java:172)
 at org.jboss.aop.instrument.MethodExecutionTransformer.instrument(MethodExecutionTransformer.java:136)
 at org.jboss.aop.instrument.Instrumentor.transform(Instrumentor.java:703)
 at org.jboss.aop.AspectManager.translate(AspectManager.java:909)
 at org.jboss.aop.AspectManager.transform(AspectManager.java:821)
 at org.jboss.aop.standalone.AOPTransformer.aspectTransform(AOPTransformer.java:88)
 at org.jboss.aop.standalone.AOPTransformer.transform(AOPTransformer.java:75)
 at sun.instrument.TransformerManager.transform(TransformerManager.java:122)
 at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:155)
 at java.lang.reflect.Proxy.defineClass0(Native Method)
 at java.lang.reflect.Proxy.getProxyClass(Proxy.java:504)
 at java.lang.reflect.Proxy.newProxyInstance(Proxy.java:581)
 at org.jboss.mx.util.MBeanProxyExt.create(MBeanProxyExt.java:395)
 at org.jboss.mx.util.MBeanProxyExt.create(MBeanProxyExt.java:349)
.... lots of jmx and deployer stack trace omitted

My code is correctly instrumented, so this is not a big issue for me. Still, it might indicate a programming error inside the instrumentation code.