Undefined variable

Hey All
I am new into COMSOL and i hope you guys can help me.

I get this message when a try to run the calculation :

Undefined variable.
- Variable: pA
- Geometry: geom1
- Domain: 2
Failed to evaluate Jacobian of expression.
- Expression: comp1.mat3.def.rho
- Feature: Time-Dependent Solver 1 (sol1/t1)
Is there someone you can tell my how to solve it?

My project look like the plunger example at the model page : www.comsol.com/model/electromagnetic-plunger-36671

I have attached my project
Regards Benny