Custom Dynamic DNS

[#1]

Hi guys.
This is my 1st post so I hope I've posted in the right place. Apologies if I haven't.
I am setting up my new Technicolor TG582n router and I see that it supports custom DynDNS providers. I currently have an account that is setup on my Synology NAS, but I would like to transfer the settings to my router as that stays switched on. As my NAS is switched off when not in use it is not able to update the IP in my DynDNS account when my external IP changes. I have added the settings on the Dynamic DNS Service section under Toolbox, but I get the error "There is an error with Dynamic DNS. Please check your connection and the username/password." I know the settings are correct. Does anyone have any advice?
Thanks
Langers

[#2]

Is your DDNS provider listed in the routers GUI?
If not, this may give you some ideas for assigning a custom provider via a few telnet commands.
http://npr.me.uk/telnet.html#updateddns

[#3]

Hi
Apologies that this isn't actually a solution. 
But I can confirm that the TG582n did not like my Synology DDNS config either!  There's not much to enter but everything gave the same error message. 
I didn't try npr's suggestion as my NAS stays on 24/7 so hope it works for you.
Andy