Just do what it says when it gives you a reason why it can't. What specifically does the game tell you when it doesn't work?
If you don't have %NAME%, %SEX%, or %SPECIES% in public or private description fields, makes sure it has it there. Literally those exact words with the % around them, all capitalized. Placed them where you would have your NPC's name, sex, and species normally in their description, they are basically a string variable. If you need them in the private field as well, just copy & past the public one into the private field, then add the private descriptions afterward.