Parallel function error: cannot be parallelized

Dear all,

i got mathematica notebook file where i run complex functions. Some computations take a lot of time (15 mns). I decided to use parrallelization by using cores available in order to make computing quicker.
But, when i used Parrallelize at first long computing, it displays : cannot be parralleilzed, proceeding with sequential evaluation.
Do you know how to fix it?
Best regards.

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