Error while using the "create item in another site" action

Hi,

 I try to use the "create item in another site" action to create an item in a custom list in another sitecollection. This site collection is hosted in another webapplication. I always get the following error: Create Site Specific Item Activity Object reference not set to an instance of an object.

Afterward I created a new custom list, to figure out if it has something to do with the list itself. the new list only has the standard title column. i get the same result. in other site collection I can use the action and i really don't know why it doesn't work this time.

The ULS log throws out 3 Unexpected errors when the action is executed (I removed our URL):

1st)

 (https://<webapp>/<managed path>/<sitecollection>/_layouts/NintexWorkflow/preview.aspx?ListId=641b51a9-aa49-4549-99ad-138ba8d1262e&ItemId=130&InstanceId=7668307b-e1cf-4d0a-b424-87a92c300927): Nintex.Workflow.NWActionExecutionException: Create Site Specific Item Activity ---> System.NullReferenceException: Object reference not set to an instance of an object.   
 at Nintex.Workflow.Activities.CreateSiteSpecificItemActivity.Process(NWWorkflowContext ctx, ActivityExecutionContext executionContext)   
 at Nintex.Workflow.Activities.CreateSiteSpecificItemActivity.Execute(ActivityExecutionContext executionContext)   
 at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(T activity, ActivityExecutionContext executionContext)   
 at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(Activity activity, ActivityExecutionContext executionContext)   
 at System.Workflow.ComponentModel.ActivityExecutorOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime)   
 at System.Workflow.Runtime.Scheduler.Run()     -
 -- End of inner exception stack trace --- (Build:2227)

 2nd)

WinWF Internal Error, terminating workflow Id# 7668307b-e1cf-4d0a-b424-87a92c300927

3rd)

System.NullReferenceException: Object reference not set to an instance of an object.   
 at Nintex.Workflow.Activities.CreateSiteSpecificItemActivity.Process(NWWorkflowContext ctx, ActivityExecutionContext executionContext)   
 at Nintex.Workflow.Activities.CreateSiteSpecificItemActivity.Execute(ActivityExecutionContext executionContext)   
 at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(T activity, ActivityExecutionContext executionContext)   
 at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(Activity activity, ActivityExecutionContext executionContext)   
 at System.Workflow.ComponentModel.ActivityExecutorOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime)   
 at System.Workflow.Runtime.Scheduler.Run()

It would be great if anyone could help me out with this one !!!

Thanks

Marco