Yahoo Sign up Error Code 999

Every time I tried to Sign up for a new account on yahoo, I am receiving Yahoo Error 999. I am using Google Chrome and even tried it in Firefox, but none of them works. I can still open the yahoo site but if clicked on Sign Up, it will direct me to yahoo site with error;

Sorry, Unable to process request at this time – Error 999
I cleared all the cache and browsing history, but it still didn’t work.
What can I do?
Help Please.
