mmoore5553 - You solved the problem! I read what you wrote in your post and I looked at the dog model fixed by you and then I was able to fix it by myself.
Here is a print of the bad vertex (inside the red circle) that didn't let me to convert the poly to subdiv:
I didn't understood very well what you were saying about making a clean model... Can you explain it? Are you talking about the problems I pointed in the picture above with the orange arrows. Am I right?
I'm seeing that Simply Maya it's a very nice community!
Thank you all!