Problem when executing an activity step

Hi all,
The problem is that when users execute an activity (complete task), it doesn’t continue to the following step. The state of this activity was in some cases ‘concluded’ or ‘error’.

The log shows the following error:

2012-03-27 13:30:49 GFT (Framework:WARN) - Caught throwable:
java.lang.NullPointerException
at wm.prt.tde.tdeCallback(tde.java:77)
at sun.reflect.GeneratedMethodAccessor139.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.wm.app.b2b.server.JavaService.baseInvoke(JavaService.java:439)
at com.wm.app.b2b.server.invoke.InvokeManager.process(InvokeManager.java:635)
at com.wm.app.b2b.server.util.tspace.ReservationProcessor.process(ReservationProcessor.java:46)
at com.wm.app.b2b.server.invoke.StatisticsProcessor.process(StatisticsProcessor.java:44)
at com.wm.app.b2b.server.invoke.ServiceCompletionImpl.process(ServiceCompletionImpl.java:238)
at com.wm.app.b2b.server.invoke.ValidateProcessor.process(ValidateProcessor.java:51)
at com.wm.app.b2b.server.invoke.PipelineProcessor.process(PipelineProcessor.java:171)
at com.wm.app.b2b.server.ACLManager.process(ACLManager.java:272)
at com.wm.app.b2b.server.invoke.DispatchProcessor.process(DispatchProcessor.java:30)
at com.wm.app.b2b.server.AuditLogManager.process(AuditLogManager.java:399)
at com.wm.app.b2b.server.invoke.InvokeManager.invoke(InvokeManager.java:539)
at com.wm.app.b2b.server.invoke.InvokeManager.invoke(InvokeManager.java:384)
at com.wm.app.b2b.server.ServiceManager.invoke(ServiceManager.java:234)
at com.wm.app.b2b.server.ServiceManager.invoke(ServiceManager.java:109)
at com.wm.app.b2b.server.HTTPInvokeHandler._process(HTTPInvokeHandler.java:150)
at com.wm.app.b2b.server.InvokeHandler.process(InvokeHandler.java:110)
at com.wm.app.b2b.server.HTTPDispatch.handleRequest(HTTPDispatch.java:190)
at com.wm.app.b2b.server.Dispatch.run(Dispatch.java:350)
at com.wm.util.pool.PooledThread.run(PooledThread.java:131)
at java.lang.Thread.run(Thread.java:619)

2012-03-27 13:30:49 GFT (Framework:WARN) - Caught throwable:
java.lang.NullPointerException
at wm.prt.tde.tdeCallback(tde.java:77)
at sun.reflect.GeneratedMethodAccessor139.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.wm.app.b2b.server.JavaService.baseInvoke(JavaService.java:439)
at com.wm.app.b2b.server.invoke.InvokeManager.process(InvokeManager.java:635)
at com.wm.app.b2b.server.util.tspace.ReservationProcessor.process(ReservationProcessor.java:46)
at com.wm.app.b2b.server.invoke.StatisticsProcessor.process(StatisticsProcessor.java:44)
at com.wm.app.b2b.server.invoke.ServiceCompletionImpl.process(ServiceCompletionImpl.java:238)
at com.wm.app.b2b.server.invoke.ValidateProcessor.process(ValidateProcessor.java:51)
at com.wm.app.b2b.server.invoke.PipelineProcessor.process(PipelineProcessor.java:171)
at com.wm.app.b2b.server.ACLManager.process(ACLManager.java:272)
at com.wm.app.b2b.server.invoke.DispatchProcessor.process(DispatchProcessor.java:30)
at com.wm.app.b2b.server.AuditLogManager.process(AuditLogManager.java:399)
at com.wm.app.b2b.server.invoke.InvokeManager.invoke(InvokeManager.java:539)
at com.wm.app.b2b.server.invoke.InvokeManager.invoke(InvokeManager.java:384)
at com.wm.app.b2b.server.ServiceManager.invoke(ServiceManager.java:234)
at com.wm.app.b2b.server.ServiceManager.invoke(ServiceManager.java:109)
at com.wm.app.b2b.server.HTTPInvokeHandler._process(HTTPInvokeHandler.java:150)
at com.wm.app.b2b.server.InvokeHandler.process(InvokeHandler.java:110)
at com.wm.app.b2b.server.HTTPDispatch.handleRequest(HTTPDispatch.java:190)
at com.wm.app.b2b.server.Dispatch.run(Dispatch.java:350)
at com.wm.util.pool.PooledThread.run(PooledThread.java:131)
at java.lang.Thread.run(Thread.java:619)

Thanks in advanced.