Problems with Navier-Brinkman multiphysics

Good morning. When doing the Navier-Brinkman multiphysics simulation i have the following two issues:
when doing the Navier-only solution (as per the "porous media flow" tutorial) i end up with negative pressure values


I tried also changing the values, the boundary conditions and removing the rectangle that i need as porous object, but it does not solve the issue.
Regarding the Brinkman part, it gives me this error

here are the .fea files:
NavierOnlyPlottedNoForceSimplified.fea
Navier_and_BrinkmanERRORSimplified.fea

I am unsure on whether it's possible to solve this issue, but i'd like to know at least if it's a technical isue or a mistake on my part (es. i put the wrong boundary conditions).
Thank you in advance