Cannot create workflow instance

AEM 6.0 SP2

Content can be published by administrator. (Members of Administrator group)  These users see "Publish" / "Unpublish" from the touch UI on Author.

However, Power users who are members of the Power Users group cannot publish.  These users see "Request publication" in the touch UI on Author.  However, when clicked nothing happens and an error simliar to below appears in the logs.

30.03.2016 08:34:03.111 *INFO* [0:0:0:0:0:0:0:1 [1459341243110] POST /bin/replicate.json HTTP/1.1] com.day.cq.replication.impl.ReplicatorImpl Setting up replication with options: ReplicationOptions{synchronous=false, revision='null', suppressStatusUpdate=false, suppressVersions=false, filter=null, aggregateHandler=null} 30.03.2016 08:34:03.111 *WARN* [0:0:0:0:0:0:0:1 [1459341243110] POST /bin/replicate.json HTTP/1.1] com.day.cq.replication.impl.ReplicatorImpl User Test.Power has not enough privileges to replicate /content/site/en/path/page 30.03.2016 08:34:03.122 *WARN* [pool-7-thread-9-null(null)] com.day.cq.wcm.workflow.impl.WcmWorkflowServiceImpl Cannot start request for de/activation workflow Request for Activation for /content/site/en/path/page: Cannot create workflow instance

A similar environment does not present this same issue.  In that case the "Request for Activation" workflow is correctly initiated by Power Users.

Any assistance on why this might be happening?

Thanks.