Try removing the mod, and see if it works then. If it does work, there's still something in the mod messing with it. If it doesn't work then the mod is fine, there's some other mod messing with it.

Nope it has to be fadillzzz's Secure Random Adoption Process mod because HOF gender mod works perfect letting me adopt pets just fine with no errors.

Oh really? Did you test my script on your site without installing fadillzzz's random adoption system? If it aint causing any errors for you this way, then its definitely your best interest to contact fadillzzz in person to discuss what to do with his mod.

It was in fact fadillzzz's random adoption system that was the cause of the problem. I reinstalled you gender ratio system and set a test pet to 102 and adopted a pet which it came out genderless. Your code works perfect it's the other mod that's causing the error.

Can you show me your current adopt.php and doadopt.php?
EDIT: I just installed this on my experimental site, and the mod is working fine. Also I've updated the tutorial again so that the mod won't break the promo code feature and is compatible with the gender ratio mod