across subdomain authentication failed on one subdomain while workingon other one

[saify]

Hello,

I am having a strange problem with a ASP .Net 2.0 web application
while trying to maintain authentication across subdomains.

In my web.config, I have forms authentication enables using cookies in
which I have the domain property set. When I'm going across different
subdomains everything works perfectly fine.

structure of my domain , subdomains is like this:-

abc.com (That is creating authetication with authetication cookie)

a.abc.com (That is using authetication of the domain with
authetication cookie)

b.abc.com (That is using authetication of the domain with
authetication cookie)

In one of my subdomain server i could not find the authetication
cookie, while on the other one i find authetication cookie and the
identity.IsAutheticatd returns true.

I could not figure out ther eason why it is not working on one server
and is working fine on another server at the same time. To figure out
the problem i deployed same application with same settings on both
servers, but response is different on both servers.

Please can someone guide me to resolve this issue.