Do you have any domain group policy? Posting the gpresult may help.

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Bob Lin, MS-MVP, MCSE & CNE
Networking, Internet, Routing, VPN Troubleshooting on
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"Dorel Sturm" <dodo@poleposition-sw.com> wrote in message
news:g217b1$odv$1@murphy.mediascape.de...
> Hi there,
>
> I have here a domain with this configuration:
>
> - computer A, B, C members of the same domain.
> - all three computers are running Windows XP. Computer A is running 64-bit
> version.
> - all of them are on the same local network.
> - all IP addresses are public addresses.
> - on none of the computers the Windows Firewall is enabled (in fact the
> service is stopped!)
> - on all three computers the same user is logged on (administrator rights
> on domain and each computer)
> - in control panel in System->Remote both Remote Assistance and Remote
> Desktop are enabled.
>
> The problem is that "Offer remote assistance" does not work. All the time
> I get the error "A Remote Assistance connection could not be established.
> You may want to check for network issues or determine if the invitation
> expired or was cancelled by the person who sent it." I tried everything
> possible but no help.
>
> The interesting stuff: Offer remote assistance works only from computer
> B!!! From B to A or C works OK but never ever from computer A to B or C or
> from C to A or B!!! There are no differences regarding network
> connections, domain membership between computer A and B.
>
> Remote desktop work correctly from any computer to any computer.
>
> When I start "Offer Remote Assistance" from computer A and I enter in the
> first line the IP address of computer B and I press Connect I get the
> correct logged on user name on computer B (I checked this by using
> different users). So the connection to computer B is OK. But when I press
> Start Remote Assistance button I get the error.
>
> Any ideas?
>
> Thanks for your help.
>
>
>