Error: 'Could not generate CMMN model'


As a try-out I have worked on a small model in Flowable modeler to create a case model. I have validated the model and checked it again whether I have everything in place. Nothing seems to be wrong in the model itself. Nor have I tried anything with custom coding so that should not be the problem. At least, I hope it is not the model.

I cannot export the model, if I try this, I get the error:
This site is not accessible
The web page at http: // localhost: 8080 / flowable-modeller / app / rest / models / fd08b5f4-c567-11e8-9394-7e7a914df67a / cmmn? Version = 1538575557797 may have been temporarily disabled or permanently moved to a new web address.

Anyway, when I try to define the app so I can start a process in the flowable-task workflow, it gives me the error ‘Could not generate CMMN model’.

Does anyone have a solution for this, or know where the problem is?

Thanks in advance