Remote Desktop Connection freezes after successful logon to Windows XP RDP

This is the most bizarre thing I've ever seen.  So, good luck Experts!  Here we go.
In City A, I have a 3 Windows XP Professional PCs. 1 with remote desktop enabled and all appropriate IP and Linksys firewall port forwarding configured.  I can successfully connect remotely to that PC from my office and several other locations tested.

In City B, I have 1 Windows XP Professional PC.  These 4 PCs are new Dell Optiplex units.  When I try to remote into the computer in City A from City B, the logon is successful, then the remote desktop freezes.  If I leave it alone, I'll get the occasional "red X" like the connection dropped, but it still says open and frozen.  Also, I can succussfully disconnect by clicking the X of the Remote Desktop window.

That is the problem.  HOWEVER...
The computer in City B can successfully and consistently remote into any other remote computer at any other office.  It only freezes when remoting into City A's PC.

I can successfully and consistenly remote into City A's PC from any location other than City B's PC.

To top it all off - I put the OLD windows 98 PC back on the network in City B, downloaded Remote Desktop Connection software and the Windows 98 PC successfully and consistently connects to the PC in City A!!

What in the world is going on here?  I've hit every variable I can think of - IP addressing, Computer Names, Workgroup Names, Registry keys, XP Firewall stuff, new user/profiles, etc.  It simply makes no sense.  Why can I sit here at home and connect to City A?  Why can the Windows 98 PC connect to City A?  Yet, the Windows XP PC right next to the Windows 98 PC freezes immediately after logon to the City A PC!  And don'f forget, the XP PC in City B can remote into every other office I support that uses RDP.  I've tried absolutely every variable EXCEPT...
I have not tried remoting into a different PC in City A.

So try to figure this out and I'll try another PC in the morning.
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The only time I've seen weird behaviour like this was when the MTU was messed up. Been doing any 'tweaking' at all or removed any network/security software?
Either way, download DRTCP:

...and try manually setting the MTU on suspect machine to 1500 or whatever the other machines are using.
Keep us posted :)

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Alan Huseyin KayahanCommented:
        Hi jcampanali
                    *What happens when a PC, which is in the same network of that CityA, try to establish RDP into that PC?
If you are totally not able do Remote Desktop from XP system in City B to City A, it must be some problem with the Xp Desktop firewall or the port No 3389 & 3390 (which is used by the RDP for transaction between the systems) is not allowed in the router/firewall of City A and City B.  But in your case as you mentioned you are able to do the RDP from Win 98 system, i suggest you to check the Xp firewall settings or the RDP version used in the XP systems.
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jcampanaliAuthor Commented:
I am doing further testing today.  Regarding the last comment, firewall settings are not an issue.  The PC that drops the connection into City A can connect to every other RDP session I try without fail.  Plus, when it does connect to City A, it doesn't actually disconnect.  It just freezes.  The session is actually still active.  I can leave the window open and scroll up and down, but clicking on Icons or the start Button does nothing.  Periodically, I'll get a quick red X, but then the connection comes back immediately, but still frozen.  I am going to try to RDP into a different PC in the same office.
Sounds almost like a "lag" issue.
Can you click on a remote icon (select it), walk away for 10 minutes, then come back and have it selected? (i.e. it took forever to send the click and refresh the local screen to reflect the change)
If it is a lag issue, updat the NIC drivers on BOTH machines (and check firmware on switches and routers between)
Also, have you tried VNC (instead of remote desktop)?
jcampanaliAuthor Commented:
The icon is never selected.  Tried that.
VNC works, but the goal was to remove the use of "extra" software. They were using Win98 and PCAnywhere 10 before the upgrade.
Try to eliminate variables:
1) In the remote desktop connection / options / advanced tab / server authentication:
select "warn" or " do not connect" (This will eliminate logon / permission issues).
2) Turn off any firewall on both PC's (temporaroly of course) to eliminate that variable.
3) If you can, Have someone in City A remote into the PC in question (on the same LAN, thus eliminating the internet variable).

Also: "what" freezes? the remote session or the entire "client" PC or is it the "server" pc that freezes.. can you have someone use the PC while the remote desktop is frozen?

(side thought: How much ram is in the remoe PC.. is this a resource issue??)
jcampanaliAuthor Commented:
None of the above.  I knew the doc had old routers in both places, so I was leaning toward the MTU issue.  In fact, one of the routers, a DLink DI-804 would not let me set it past 1492, so setting the PCs to 1500 would do no good.  We tried a separate PC and it didn't work either.  We tried remoting from City A into City B and got the SAME PROBLEM.  Thanks drmarston.  So, why could the suspect PC remote into all my other folks??  Who the heck knows.  Why does the Win98 PC work fine from City A to City B.  Answer: Win98 isn't smart enough to detect any connection problems.
So, I had a not so old Linksys sitting in the truck - swapped out routers and now everything works in both places.  What a joke.
Thanks for your help everyone.
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