what does the error "The task cannot be deleted since it is referred by the task(s)" mean?

this case has been encountered after following the steps below:
-do a clean server with delete.all.relations=true
-import-object-set
-send to server the Synchrony server

then the following error occurs:

FATAL  :20090316:16.59.23:InitBroadcastAction(XibContext):core.cfgserver.CfgServerValidateFailException: The task cannot be deleted since it is referred by the task(s)
core.cfgserver.CfgServerValidateFailException: The task cannot be deleted since it is referred by the task(s)
at core.cfgserver.CfgServer.deleteRecords(CfgServer.java:2298)
at core.cfg_core.CfgTask.deleteRecords(CfgTask.java:441)
at com.axway.xd.broker.xib.broadcast.agent.adapter.XibContext.deleteTask(XibContext.java:2162)
at com.axway.xd.broker.xib.broadcast.agent.adapter.XibContext.deleteNetAdapterTask(XibContext.java:2211)
at com.axway.xd.broker.xib.broadcast.agent.adapter.XibContext.deleteNetAdapterTask(XibContext.java:2177)
at com.axway.xd.broker.xib.broadcast.agent.action.SendToServerBroadcastAction.sendToServerXSoftwareXib(SendToServerBroadcastAction.java:658)
at com.axway.xd.broker.xib.broadcast.agent.action.SendToServerBroadcastAction._sendToServer(SendToServerBroadcastAction.java:316)
at com.axway.xd.broker.xib.broadcast.agent.action.SendToServerBroadcastAction.run(SendToServerBroadcastAction.java:129)
at com.axway.xd.broker.xib.broadcast.agent.XibAgent.commit(XibAgent.java:317)
at com.axway.framework.business.diffusion.EngineExploitThread.run(EngineExploitThread.java:84)

Look at the task monitor in copilot and to the coreTasks panel in the composer, perhaps a task has not been created by the import-object-set. If this is the case, to avoid this, create a new task with the same name or rename one in the coreTasks panel, and do again:

-clean server with delete.all.relations=true
-import-object-set
-send to server the Synchrony server