User Task Not Found Exception using BDM in Bonita ui

I have developed test application using BDM and Bonita ui designer in Bonita BPM Community Edition Version : 7.3.1. I have business object named “BusinessObject1” with one string type name and “namebd” as Business Variables of “BusinessObject1”.
In Step1 i created one Input:

formInput | {“nameInput” : {“name” : “”}} | JSON
in step1 operations i added:
namebd steName nameInput.name

In step2 i created one input :
taskId id URL parameter
task …/API/bpm/userTask/{{taskId}} External API
context …/API/bpm/userTask/{{taskId}}/context External API
namebd …/{{context.namebd_ref.link}} External API

Error Log:
2016-12-04 09:43:12.531 -0800 WARNING: org.restlet.Component.BonitaRestletApplication Exception or error caught in server resource
org.bonitasoft.engine.bpm.flownode.UserTaskNotFoundException: USERNAME=walter.bates | Activity instance with id 7675984443287227753 not found
at org.bonitasoft.engine.api.impl.ProcessAPIImpl.getUserTaskContract(ProcessAPIImpl.java:5678)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.bonitasoft.engine.api.impl.ServerAPIImpl.invokeAPI(ServerAPIImpl.java:462)
at org.bonitasoft.engine.api.impl.ServerAPIImpl$2.call(ServerAPIImpl.java:431)
at org.bonitasoft.engine.transaction.JTATransactionServiceImpl.executeInTransaction(JTATransactionServiceImpl.java:312)

2016-12-04 10:44:46.291 -0800 SEVERE: org.bonitasoft.web.rest.server.api.resource.CommonResource org.bonitasoft.engine.bpm.data.DataNotFoundException: USERNAME=walter.bates | org.bonitasoft.engine.core.process.instance.api.exceptions.SFlowNodeNotFoundException: Flow node instance with id 4002 not found
org.bonitasoft.web.toolkit.client.common.exception.api.APIException: org.bonitasoft.engine.bpm.data.DataNotFoundException: USERNAME=walter.bates | org.bonitasoft.engine.core.process.instance.api.exceptions.SFlowNodeNotFoundException: Flow node instance with id 4002 not found
at org.bonitasoft.web.rest.server.api.bpm.flownode.ActivityVariableResource.getTaskVariable(ActivityVariableResource.java:28)

Caused by: org.bonitasoft.engine.bpm.data.DataNotFoundException: USERNAME=walter.bates | org.bonitasoft.engine.core.process.instance.api.exceptions.SFlowNodeNotFoundException: Flow node instance with id 4002 not found

Please follow this video for getting started. It will guide you through all the process and you will find your answer there.
http://www.bonitasoft.com/resources/videos/getting-started-tutorial