Low accuracy of the radiated power calculation: error in CST

Hi! I am using Multilayer solver for Characteristic Mode Analysis in CST Studio, I have to calculate far fields and radiation patterns along with the surface currents, but during Field Monitor Calculations it is giving me an error
"Low accuracy of the radiated power calculation: nan. Desired accuracy is 0.005."

Can anyone explain to me why I am getting this error and how to resolve this issue

Regards