"Remote Assistance Cannot Connect"

>I get the following error when I try to establish a Remote Assistance
>Session (novice requesting help from me):
>
> "Remote Assistance Cannot Make the Connection. The remote user user may
> have disconnected".
>
> Both systems are Vista, running the latest version of Windows Live
> Messenger (8.5.1302.1018). Both systems are behind routers, but each has
> UPnP enabled: WLM Connection Status states "You are connected to the
> Internet though a uPNP port-restricted NAT". Windows Firewall is OFF and
> there is no antivirus firewall. In System Properties, "Allow Remote
> Assistance.." is checked.
>
> After trying to connect, both systems are prompted to type a password, but
> the error comes up after passwords are entered.
>
> Interestingly, if *I* make the request for remote assistance from the
> "novice" system, everything connects perfectly.
>
> Any ideas - I have googled this for hours? Do I have to setup port
> forwarding if uPNP is working as it appears to be??
> Thanks
>