Error when querying CRM with Nintex WF 2013

I am trying to build a workflow for a client which, based on information in a SharePoint list, creates/updates entities in CRM 2011. However in the phase "Query CRM" the workflows throws the error

"Workflow action 'Nintex.Workflow.Activities.QueryCRMSequenceActivity' is not allowed on site http://...."

I have checked in the "Manage Allowed Actions" and all the possible actions are checked (in both Site Collection and Central Admin), moreover I cannot see any action containing the value "QueryCRMSequenceActivity".

I have tried to do different things in in the "Query CRM" action (i.e. tried to create different type of entities) but I still get the same error.

Any idea?

Thanks

Vincent