Single sign on problem with Multidomain

I have installed my site http://www.chotecelebs.com and installed Multi domain and enabled "single sign on" option

And my Sub domains are
http://www.chotecelebs.com/contest-3-5-years/
http://www.chotecelebs.com/contest-6-8-years/

Problem:
when i login to my main site then my sub sites are not signing in

Please help me in solving this problem