Problem with cookie

I have a home page runnig a forum at http://b.domaindlx.com/izerr/ everything works fine when i use this url to visit the forum and page.. The forum remembers me throughout using a cookie.... but when i use a short url www.izer.tk which redirects a user to the above home poage... The login system does not seem to log me properly... Even after loging in it shows the login screen... So how do i solve this problem...

Cookies are only accesible by the domain name which created them.

so there!

and let's not forget about our shinny new tech board either

so how do i solve the problem...