Circular variable dependency detected

Hi,
I am trying to solve a problem of a 3D acoustic perforated panel under un incident plane wave.
When running the simulation, i get this error:
"the following feature has encountered a proble:
Circular variable dependency detected.
-variable: mod1.Z
-Geometrie: 1
-Point: 18
-Feature stationary solver 1 (sol2/s1)
-Error: Circular variable dependency"
Can anybody help me to solve this?

Amadou