I'm getting this error on a ping() method invoked form client app. every 10min:
I'm using JBoss 4.2.3GA and I had this issue only form time to time for one of the deployments.

NFO | jvm 1 | 2009/02/12 12:59:45 | 12:59:45,495 ERROR [LogInterceptor] EJBException in method: public abstract void com.pb.ejb.interfaces.PbUserService.ping() throws com.pb.base.PbException,java.rmi.RemoteException:
INFO | jvm 1 | 2009/02/12 12:59:45 | javax.ejb.EJBException: Application Error: no concurrent calls on stateful beans
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.plugins.StatefulSessionInstanceInterceptor.invoke(StatefulSessionInstanceInterceptor.java:307)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.plugins.CallValidationInterceptor.invoke(CallValidationInterceptor.java:63)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:121)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:350)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:181)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:205)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:138)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.SessionContainer.internalInvoke(SessionContainer.java:648)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.ejb.Container.invoke(Container.java:960)
INFO | jvm 1 | 2009/02/12 12:59:45 | at sun.reflect.GeneratedMethodAccessor201.invoke(Unknown Source)
INFO | jvm 1 | 2009/02/12 12:59:45 | at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
INFO | jvm 1 | 2009/02/12 12:59:45 | at java.lang.reflect.Method.invoke(Method.java:597)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:155)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.server.Invocation.dispatch(Invocation.java:94)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.server.Invocation.invoke(Invocation.java:86)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:659)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.invocation.unified.server.UnifiedInvoker.invoke(UnifiedInvoker.java:231)
INFO | jvm 1 | 2009/02/12 12:59:45 | at sun.reflect.GeneratedMethodAccessor200.invoke(Unknown Source)
INFO | jvm 1 | 2009/02/12 12:59:45 | at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
INFO | jvm 1 | 2009/02/12 12:59:45 | at java.lang.reflect.Method.invoke(Method.java:597)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:155)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.server.Invocation.dispatch(Invocation.java:94)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.server.Invocation.invoke(Invocation.java:86)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:659)
INFO | jvm 1 | 2009/02/12 12:59:45 | at javax.management.MBeanServerInvocationHandler.invoke(MBeanServerInvocationHandler.java:288)
INFO | jvm 1 | 2009/02/12 12:59:45 | at $Proxy16.invoke(Unknown Source)
INFO | jvm 1 | 2009/02/12 12:59:45 | at org.jboss.remoting.ServerInvoker.invoke(ServerInvoker.java:769)


is this a Jboss bug?