DynDNS and DD-WRT - Error validating DYNDNS svr answer

I have DD-WRT v24-sp2 and I had to spend some time trying to get DynDNS configuration working. The DD-WRT wiki for DDNS seems a bit confusing... but here's how to fix the error below:

"W:INADYN: Error validating DYNDNS svr answer. Check usr,pass,hostname! (HTTP/1.1 200 OK" 

Complete your DDNS configuration with the following information:

DDNS Service: Custom
Do not use external IP check: No
DYNDNS Server: members.dyndns.org (you do need the members subdomain)
User Name: [ your user name - usually not email ]
Password: [ your password ]
Host Name: [ your hostname as it shows on your account - usually hostname.dyndns.org ]
URL: /nic/update?
Additional DDNS Options: --dyndns_system dyndns@dyndns.org --ip_server_name checkip.dyndns.org:8245 /

Click on "Save" and then on "Apply Settings". You should see a sucessfull update at the status:

Sat Jul 27 16:59:37 2013: INADYN: Started 'INADYN Advanced version 1.96-ADV' - dynamic DNS updater. 
Sat Jul 27 16:59:37 2013: I:INADYN: IP address for alias 'fakehost.dyndns.org' needs update to '1.1.1.1' 
Sat Jul 27 16:59:37 2013: I:INADYN: Alias 'fakehost.dyndns.org' to IP '1.1.1.1' updated successfully.