I have a method which takes java.sql.Connection from connection pool do some operation on DB and then close connection (i.e. return to the pool). There are multiple threads which are executing this method. Every time I execute this in multithreaded environment I get java.lang.IllegalAccessException: Failed to find connection exception on line connection.prepareStatement(query) of my class. But this issue goes away if I synchronize (on class object) code block which closes DB connection. I am using MySQL Connector/J 5.1.10 JDBC driver. Following is a exception trace:

Caused by: java.lang.IllegalAccessException: Failed to find connection: 2365173
at org.jboss.resource.adapter.jdbc.remote.WrapperDataSourceService.invoke(WrapperDataSourceService.java:212)
at sun.reflect.GeneratedMethodAccessor283.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:157)
at org.jboss.mx.server.Invocation.dispatch(Invocation.java:96)
at org.jboss.mx.server.Invocation.invoke(Invocation.java:88)
at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:668)
at org.jboss.invocation.jrmp.server.JRMPInvoker$MBeanServerAction.invoke(JRMPInvoker.java:855)
at org.jboss.invocation.jrmp.server.JRMPInvoker.invoke(JRMPInvoker.java:422)
at sun.reflect.GeneratedMethodAccessor282.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:305)
at sun.rmi.transport.Transport$1.run(Transport.java:159)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:155)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:535)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:790)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:649)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknown Source)
at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source)
at sun.rmi.server.UnicastRef.invoke(Unknown Source)
at org.jboss.invocation.jrmp.server.JRMPInvoker_Stub.invoke(Unknown Source)
at org.jboss.invocation.jrmp.interfaces.JRMPInvokerProxy.invoke(JRMPInvokerProxy.java:133)
at org.jboss.invocation.InvokerInterceptor.invokeInvoker(InvokerInterceptor.java:365)
at org.jboss.invocation.InvokerInterceptor.invoke(InvokerInterceptor.java:197)
at org.jboss.proxy.ClientMethodInterceptor.invoke(ClientMethodInterceptor.java:74)
at org.jboss.proxy.ClientContainer.invoke(ClientContainer.java:101)
... 15 more