It is normal that you cannot connect to the hotspot’s admin page wirelessly after hotspot setup. This is because you should have a valid username and password for the hotspot, otherwise you cannot access any page, other than www.hotspotsystem.com .
Related article: Use your own internet without restrictions
DD-WRT related issue: If this is happening just after you upgraded to DD-WRT (and you didn’t do the setup yet) it is probably because the httpd process was crashing every time I tried to access it.
Telnet or ssh into WRT, then type:
nvram set language=english
You may also need to do the following to get in from a browser:
nvram set http_psswd=””
Visit this page for more information about the issue.