poroelastic pellicle squeezed at a constant rate: unknown error

Hi

I am trying to simulate the squeezing of a poroelastic pellicle under two flat plates at a constant squeezing rate. However, an error comes up and I really don’t understand the reason. The error is as follows:

Failed to evaluate variable.
- Variable: mod1.poro.uInitZ
- Geometry: 1
- Boundary: 4
Failed to evaluate expression.
- Expression: mod1.poro.uInitZ

Could you give me a hint on this? The model is attached.

Thanks