DNS name could not be resolved [RA+WM]

Am trying to setup a Remote Assistance connection but receive an error
message: ‘DNS name could not be resolved’ – under the following conditions.

1. OS’s are WinXPro and WinXPHome
2. TCP/IP is set DHCP and DNS enabled.
3. Both using Windows Messenger 5.1 (and don’t want to upgrade).
4. Both computers can ping each other across the internet.
5. Registry settings a
a. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\Terminal Server
AllowTSConnections 1
b. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Ole EnableDCOM Y
c. HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Mes senger\Client PreventAutoRun 0 PreventRun 0
6. Control Panel\System\Remote set to allow Remote Assistance and allow
remote control.
7. Group Policy not configured on WinXPro machine.
8. Windows Firewall program exceptions a
a. Remote Assistance
b. Remote Assistance Windows Messenger and Voice
c. Remote Desktop
d. Windows Messenger
e. Helpsvc.exe and Helpctr.exe
9. Windows Firewall ports open a
a. TCP 135
b. TCP 3389
c. AV/AS/WB/FT not required (for the moment).
10. Both routers a
a. UPnP enabled
b. in DHCP server mode
c. in DNS mode
d. Firewalls disabled

Seems like the UPnP function is not working? Or is it something more basic
than that? Thanks …