Engr. Faraz Ahmad can you please provide more information on the error, your mesh and problem statements.

The procedure for setting up and solving a radiation problem is outlined below, and described in detail in referenced sections. Steps that are relevant only for a particular radiation model are noted as such. Remember that the steps that are pertinent to radiation modeling, only, are shown here. For information about inputs related to other models that you are using in conjunction with radiation, see the appropriate sections for those models. Activate radiative heat transfer by selecting a radiation model ( Rosseland, P1, Discrete Transfer (DTRM), Surface to Surface (S2S), or Discrete Ordinates) under Model in the Radiation Model dialog box

Thanks alot hamed azimi for your precious answer