I created a subdomain, and linked it in inside the IIS manager. It works fine, here the problem ... I can view the subdomain page from the outside, but locally on the domain I cannot.
Sounds like your internal DNS isnt updated correctly... What happens when you try to ping the subdomain? Does it time out/Unknown host/ or list the correct IP of the server?
from the command prompt : ping subdomain.yourdomain.com <hit enter>