Remote Assistence on 3G and ADSL

[3GisDaMan]

I am trying to help someone sort their PC out. They have a WebAfrica ADSL account, and me use 3G. I receive the Remote Assistence e-mails, but when we try to connect, the following error message is displayed:

Remote Assistance connection could not be established because the remote host name could not be resolved. Please try again.

Both Win XP SP2.
I have switched of both firewalls, still no luck.
Remote assistence is enabled on both firewalls, and in both REMOTE tabs in SYSTEM.

HELP!

 

[MobileAllOver]

Try using their IP address...

I haven't used Remote Assistance though. Did experiment with a web-based P2P remote assistance program but can't remember the name.

 

[3GisDaMan]

Tried, didn't work. The IP is the same as in the file.
I can't ping the machine either.