rule not found while parsing element

I need again some help:
I have a scenario (OAS) in which some messages are submitted to a condition:
Mechanical energy transmission occurs when the clutch is closed
Then, I’m using a constraint which is mentioned in the exchange context box.
The opaque expression is now named without space, ant the text refers to exchange items and linked data
The point is while transforming into OES, I have the answer “rule not found while parsing element” where the element is the constraint.
My solution would be to place an ALT fragment instead, but I will need again to use the constraint, may be to build the opposite one and place it in the operand data…
Or may be the constraint shall be stored in particular place: at the moment, OA/Data is not yet structured and constraints are there.
Thanks you for answers.

Since this time I had again the same issue today. I finally manage to find the reason:
The constraint has to locate in the tree under the scenario in which the messages are, and not in the data folder where all were.
Still I have moved the condition from messages to fragments operands before finding it.
Thanks for your time

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