BPMN collaboration model assigment

Hi

I am trying to create a new assignment function ( vac) from BPMN collaboration model.

The function already have one association with other BPMN collaboration model, so this type of model do not appear in options for me. I have tryed to create using a script, but is not working.

There any solution for this problem?

I saw that for EPC models I can create a lot of associations.

Thanks a lot

Priscila