Windows Messenger SIP connectivity error

[Guest]

I am running Windows Messenger 5.1.0701 at home. I am only able to sign into
the NET messaging service. I want to also be able to sign into the SIP
communication service because most of my contacts are on that at their work.
Unfortunately, I get an error message that says, "an HTTPS or TCP connection
could not be made. Please contact your administrator or try again later." I
sometimes also get one that says "the specified email address (mine that
works fine for .net) is invalid or the service is currently unavailable."
when I try to sign into SIP.

Up until very recently I was able to instant message with these people with
no trouble at all. I just typed in their email address where you Add A
Contact and it was fine. Then one day I appeared offline to them and they to
me even though to our knowledge there were no server or technical changes on
either end. I eventually uninstalled and reinstalled Messenger but that has
not helped.

Is there an easy way for me, at home, using my hotmail address that I've
always used for this, to be able to add these SIP people as contacts and IM
with them? I apologize if I'm missing something obvious and would be happy to
provide any more information to the best of ability if it's needed. Thank you.

 

[Guest]

I have experienced this exact same issue as described below and am pulling my
hair out trying to locate the solution. I split time between working at home
and in the office. The odd part is that when in the office on the local LAN,
the issue goes away.