Validation error: "It cannot be more than one connector between the same two elements"

I am trying to model one of our processes, and in this model, different tasks in different pools in the same milestone should be connected by message flow connectors to show that they send and receive messages. My problem is although this seems logical, I keep getting the error message of "It cannot be more than one connector between the same two elements" whenever I want to validate the process. Another problem is when I create the exact process model on another computer, it doesn't show the error. So, now I am confused about this kind of connection. Are we allowed to have two connectors between two elements in different pools or not?

Comments (2)


Dear Mehr,

Thank you for your questions. Looking at the image you sent, we can say that the error does not happen because of the message flows between the multiple sub processes located in different processes within your diagram.

The error you mention occurs because the third sub process in the process called "Host1" has 2 sequence flows (one that goes to an end event, and one that goes back to the first sub process in the sequence). The Modeler reports an error because this modeling does not comply with the BPMN standard as in real life, there's no way of knowing which way the sequence should go. Thus, if you need the option to go back to be available, you need to include an exclusive gateway after the third sub process that will evaluate the condition to choose either to go back or to finish the process.

Best regards,

Laura G


Dear Laura,

Thank you so much for answering my question. I tried your approach and deleted the line that go back to the previous task, but still I get the same error. Also, the validation error that I get is 12 error messages and I have 12 message flows between different sub-processes. When I click on the error messages it shows me the message flow that have problem and bold it. I attached a picture to show what I mean. I would really appreciate it if you could help me with that.