some problems in my COMSOL Multiphysics model

Hi
There are some problems with my model. I build a model of the RF generator whichis a rectangular cavity and two electrodes and the sample is in the middle of the two plates. The top electrode is used as a port for radio frequency emission and the voltage is added on it. I use the joule heating module and frequency domain.
But the result is failed to calculate variable(-variable: comp1.emw.sigmabnd - defined as: material.sigmabnd; -variable: comp1.emw.Jsy- defined as: comp1.emw.tEy*sqrt((epsilon0_const*(comp1.emw.epsilonrbnd+(comp1.emw.sigmabnd/(epsilon0_const*comp1.emw.iomega))))/(comp1.emw.murbnd*mu0_const))
Failed to calculate expression(- espression: d((comp1.emw.iomega*mu0_const*(-comp1.emw.Jsx*comp1.emw.testPhystEx-comp1.emw.Jsy*comp1.emw.testPhystEy-comp1.emw.Jsz*comp1.emw.testPhystEz)/comp1.emw.Kscale)*(dvol),{test@1})
I don't know where the problem is. Please give me a detailed answer and recommendations for model。
Thank you so much~