MSSQL throws "Violation of UNIQUE KEY constraint" Exception when using Subprocesses

We were using Postgresql and did now some tests using MSSQL. All processes containing subprocesses throw the following exception:

java.sql.SQLException: Violation of UNIQUE KEY constraint 'UQ_JBPM4_EX_C4971C0E06B7F65E'. Cannot insert duplicate key in object 'dbo.JBPM4_EXECUTION'.
at net.sourceforge.jtds.jdbc.SQLDiagnostic.addDiagnostic(SQLDiagnostic.java:368)
at net.sourceforge.jtds.jdbc.TdsCore.tdsErrorToken(TdsCore.java:2816)
at net.sourceforge.jtds.jdbc.TdsCore.nextToken(TdsCore.java:2254)
at net.sourceforge.jtds.jdbc.TdsCore.getMoreResults(TdsCore.java:631)
at net.sourceforge.jtds.jdbc.JtdsStatement.processResults(JtdsStatement.java:584)
at net.sourceforge.jtds.jdbc.JtdsStatement.executeSQL(JtdsStatement.java:546)
at net.sourceforge.jtds.jdbc.JtdsPreparedStatement.executeUpdate(JtdsPreparedStatement.java:505)
at org.tranql.connector.jdbc.PreparedStatementHandle.executeUpdate(PreparedStatementHandle.java:103)
at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:94)
at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:57)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2176)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2656)
at org.hibernate.action.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:71)
at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:279)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:321)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:204)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:130)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:563)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:551)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:547)
at org.jbpm.pvm.internal.model.DefaultIdGenerator.createId(DefaultIdGenerator.java:41)
at org.jbpm.pvm.internal.model.ExecutionImpl.initializeProcessInstance(ExecutionImpl.java:184)
at org.jbpm.pvm.internal.model.ProcessDefinitionImpl.createProcessInstance(ProcessDefinitionImpl.java:107)
at org.jbpm.jpdl.internal.activity.SubProcessActivity.execute(SubProcessActivity.java:69)
at org.jbpm.pvm.internal.model.op.ExecuteActivity.perform(ExecuteActivity.java:60)
at org.jbpm.pvm.internal.model.ExecutionImpl.performAtomicOperationSync(ExecutionImpl.java:637)
at org.jbpm.pvm.internal.model.ExecutionImpl.performAtomicOperation(ExecutionImpl.java:597)
at org.jbpm.pvm.internal.model.ExecutionImpl.start(ExecutionImpl.java:201)
at org.jbpm.pvm.internal.cmd.StartProcessInstanceInLatestCmd.execute(StartProcessInstanceInLatestCmd.java:65)
at org.jbpm.pvm.internal.cmd.StartProcessInstanceInLatestCmd.execute(StartProcessInstanceInLatestCmd.java:38)
at org.jbpm.pvm.internal.svc.DefaultCommandService.execute(DefaultCommandService.java:42)
at org.jbpm.pvm.internal.spring.CommandTransactionCallback.doInTransaction(CommandTransactionCallback.java:50)
at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:130)
at org.jbpm.pvm.internal.tx.SpringTransactionInterceptor.execute(SpringTransactionInterceptor.java:77)
at org.jbpm.pvm.internal.svc.EnvironmentInterceptor.execute(EnvironmentInterceptor.java:46)
at org.jbpm.pvm.internal.svc.RetryInterceptor.execute(RetryInterceptor.java:55)
at org.jbpm.pvm.internal.svc.ExecutionServiceImpl.startProcessInstanceByKey(ExecutionServiceImpl.java:78)
at com.softmodeler.service.impl.WorkflowService.start(WorkflowService.java:130)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.doInvoke(ServiceInvoker.java:58)
at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.invoke(ServiceInvoker.java:62)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invokeUnprivileged(ServiceTCCLInterceptor.java:56)
at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invoke(ServiceTCCLInterceptor.java:39)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.osgi.service.importer.support.LocalBundleContextAdvice.invoke(LocalBundleContextAdvice.java:59)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
at $Proxy68.start(Unknown Source)
at com.softmodeler.service.impl.BasicObjectRefService.createAndStartWorkflow(BasicObjectRefService.java:467)
at com.softmodeler.service.impl.BasicObjectRefService.commit(BasicObjectRefService.java:505)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.riena.communication.core.hooks.AbstractHooksProxy.invoke(AbstractHooksProxy.java:69)
at org.eclipse.riena.communication.core.hooks.AbstractHooksProxy.invoke(AbstractHooksProxy.java:38)
at org.eclipse.riena.internal.communication.publisher.ServiceHooksProxy.invoke(ServiceHooksProxy.java:71)
at $Proxy71.commit(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.caucho.hessian.server.HessianSkeleton.invoke(HessianSkeleton.java:180)
at com.caucho.hessian.server.HessianSkeleton.invoke(HessianSkeleton.java:109)
at org.eclipse.riena.communication.publisher.hessian.RienaHessianDispatcherServlet.service(RienaHessianDispatcherServlet.java:148)
at org.eclipse.equinox.http.registry.internal.ServletManager$ServletWrapper.service(ServletManager.java:180)
at org.eclipse.equinox.http.servlet.internal.ServletRegistration.handleRequest(ServletRegistration.java:90)
at org.eclipse.equinox.http.servlet.internal.ProxyServlet.processAlias(ProxyServlet.java:111)
at org.eclipse.equinox.http.servlet.internal.ProxyServlet.service(ProxyServlet.java:67)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
at org.eclipse.equinox.http.jetty.internal.HttpServerManager$InternalHttpServiceServlet.service(HttpServerManager.java:318)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:502)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:380)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:324)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:535)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:880)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:835)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:213)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:520)

The exception is thrown in DefaultIdGenerator.createId() when calling session.save() of the ExecutionImpl. At that point ExecutionImpl does not have an ID. We use JTA Transaction types see attachment maybe this is the cause of the issue?