Cannot run a process

Hi All, I am new to bonita and get this error when trying to run a process. Details are as below: I have configured server settings and authentication using same username as admin. Also I added it in the organisation. What else should I do? Thanks in advance its 6.3.8 version

ERROR USERNAME=admin | The return type of the expression must be Boolean !STACK 0 org.bonitasoft.engine.exception.BonitaRuntimeException: USERNAME=admin | The return type of the expression must be Boolean at org.bonitasoft.engine.api.HTTPServerAPI.invokeMethod(HTTPServerAPI.java:143) at org.bonitasoft.engine.api.impl.ClientInterceptor.invoke(ClientInterceptor.java:88) at com.sun.proxy.$Proxy23.deploy(Unknown Source) at org.bonitasoft.studio.engine.operation.DeployProcessOperation.deployProcess(DeployProcessOperation.java:189) at org.bonitasoft.studio.engine.operation.DeployProcessOperation.deploy(DeployProcessOperation.java:164) at org.bonitasoft.studio.engine.operation.DeployProcessOperation.run(DeployProcessOperation.java:117) at org.bonitasoft.studio.engine.command.RunProcessCommand$1.run(RunProcessCommand.java:224) at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:121) at < ========== Beginning of the server stack trace ========== >. ( ) at org.bonitasoft.engine.bpm.bar.xml.XMLProcessDefinition.fillExpressionNode(XMLProcessDefinition.java:1004) at org.bonitasoft.engine.bpm.bar.xml.XMLProcessDefinition.fillTransitionNode(XMLProcessDefinition.java:1025) at org.bonitasoft.engine.bpm.bar.xml.XMLProcessDefinition.createAndFillFlowElements(XMLProcessDefinition.java:435) at org.bonitasoft.engine.bpm.bar.xml.XMLProcessDefinition.getXMLProcessDefinition(XMLProcessDefinition.java:394) at org.bonitasoft.engine.bpm.bar.ProcessDefinitionBARContribution.serializeProcessDefinition(ProcessDefinitionBARContribution.java:271) at org.bonitasoft.engine.bpm.bar.ProcessDefinitionBARContribution.saveToBarFolder(ProcessDefinitionBARContribution.java:264) at org.bonitasoft.engine.bpm.bar.BusinessArchiveFactory.writeBusinessArchiveToFolder(BusinessArchiveFactory.java:134) at org.bonitasoft.engine.api.impl.ProcessAPIImpl.unzipBar(ProcessAPIImpl.java:818) at org.bonitasoft.engine.api.impl.ProcessAPIImpl.deploy(ProcessAPIImpl.java:739) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:483) at org.bonitasoft.engine.api.impl.ServerAPIImpl.invokeAPI(ServerAPIImpl.java:368) at org.bonitasoft.engine.api.impl.ServerAPIImpl$1.call(ServerAPIImpl.java:337) at org.bonitasoft.engine.transaction.JTATransactionServiceImpl.executeInTransaction(JTATransactionServiceImpl.java:276) at org.bonitasoft.engine.api.impl.ServerAPIImpl.invokeAPIInTransaction(ServerAPIImpl.java:344) at org.bonitasoft.engine.api.impl.ServerAPIImpl.invokeAPI(ServerAPIImpl.java:286) at org.bonitasoft.engine.api.impl.ServerAPIImpl.invokeMethod(ServerAPIImpl.java:128) at org.bonitasoft.engine.api.internal.servlet.HttpAPIServletCall.doPost(HttpAPIServletCall.java:112) at org.bonitasoft.engine.api.internal.servlet.HttpAPIServlet.doPost(HttpAPIServlet.java:35) at javax.servlet.http.HttpServlet.service(HttpServlet.java:643) at javax.servlet.http.HttpServlet.service(HttpServlet.java:723) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.bonitasoft.console.security.SessionFixationValve.invoke(SessionFixationValve.java:77) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Thread.java:745)