Some users can't see login page

I have set up a hotspot using a RB450G with V5.8. Some users can login succesfully but some users can’t see login page.
When they type any page like Yahoo.com or other one, the address bar change to myhotspot/login… But some guests only receive a page error, like the page does not exist. It looks like some machines can’t recognize “myhotspot” local domain, but other ones can.
Please help!!!

Most of my test computers had a problem if that was not a FQDN. You should try a FQDN, like
myhotspot.mydomain.com

Sorry, but what is a FQDN?
Usually any computer must be able to login, with no changes, isn’t it?
I can’t made modifications in client’s computers.

No changes in the client computer. This would be in

/ip hotspot profile
set X dns-name="hotspot.mydomain.com"

A Fully Qualified Domain Name has at least two parts, but most browsers will require three for this.
Like these examples:
mydomain.com
www.mydomain.com
hotspot.mydomain.com

www and hotspot are the servers in that domain (hotspot will be your router). The domain is mydomain.com.