Hello Morten,
Sorry for the confusion, but we are not sure what the workflow is. The thing is that the Move Web interface action does not have a form at all. While according to the screenshots, your action does have a form. Also, the ParentDN property can only be added to the View form or action in Adaxes Web interface. This limitation is due to the property being calculated. It cannot be modified manually. As such, the property cannot be added, for example, to the forms used to modify objects.
For us to provide you with a possible solution, please, provide all the possible details regarding the workflow you have with live examples. If there are any business rules involved in the workflow, please, post here or send us (support@adaxes.com) screenshots.