Participate in Radiation not appearing in edit window of cell zone conditions
 

Hi mates,
I am currently doing natural convection analysis (using fluent 14) in which I want to consider the radiation heat transfer, where I used the Radiation Discrete Ordinates (DO) model. But when I go to edit window, in the cell zone conditions, the Participates in Radiation option is not appearing.

I am clueless about what is went wrong.

Please kindly help on this.

Thanking You,
Vinayaka:)