Business rule return error message

Good morning,

I created a business rule that looks like this : 


Long story short, i want value to change depending on the subject title when a case is created.

Then, in a BPM, i added this business rule under the step "Assignation en fonction du titre".
Finaly, if the a case went through one the conditions, it has to go to the "End Event #1", otherwise, it will follow another step.



However, i keep getting an error message.

What did i do wrong ?
I suspect something about the last line in the business rule ?

Thanks for your help