BPMN 2.0: Message flow is not valid

[MiniBlondie]

Hi

I'm creating a BPMN where I have a message flow going from 1 activity of one lane to an activity situated in another lane. Both lanes are located in different pools.
In some diagram, there is no issues.
In others, I get the following message: "Message flow is not valid within a pool boundary.

Visually, I don't see the differences between the diagram where it works and the others. Is it a matter of layer?

Thank you

[KP]

The lanes might not be in the pools you think they are in. Look in the Project Browser for the definitive answer.

[MiniBlondie]

Indeed. thank you