"Unable to resolve Host name" trying to give remote assistance.

[GrahamP]

I cannot provide Remote Assistance to Dad's laptop at his home. He requests
remote assistance from me, I accept the invitaion, the sytem tells me it is
trying to connect and then I get the message, "Unable to connect because I
cannto relsove the host name. Please try again". We have tried repeatedly.

History is that I had the laptop here last week and was able to establish
Remote Asssistance while both computers connected to my LAN. Both are
running Norton Internet Security which did not interfere. The laptop has now
been transported and is connected to his ADSL router, which is a NAT device
and is UPnP. Everything I've read about running Remote Assistance through
firewalls and routers suggests that this should be working just fine. All
invitations and accptances appear to be sent and received normally. The
connection is failing at the very last stage, just when the RA screens should
load on my system. Port 3389 is specifically open on both firewalls.

I'm at a loss what to do now. Can anyone point me in the right direction?
--
Why do error messages lie to me?