Sub-domains are in the format of sub1.mydomain.com or sub2.mydomain.com. If you are having problems accessing your sub-domain after creating it, it could be because of one or more of the following issues:

Your sub-domain has not yet propagated throughout the Internet. (This is similar to the mechanism your main domain had to go through when you changed your name servers for it.) Please wait the recommended 48 hours and try your sub-domain again.