Flowable UI Access Rights

Hi, I have a question regarding the flowable UI. I would like to investigate the case plan for a completed case in flowable UI. I am logging in as one the users I created but when I select the completed case and click show diagram button I receive an error. Is there a way to fix this?
Is there a way to give some users the access right to read the forms in the other running and completed cases that are not assigned to them? As it is right now, they cannot access the information in the forms of other cases.