I've been getting this 80072745 error in Windows Live Messenger second time
in 2 months. Login was impossible on all computers in network connected to
Netgear DG834N router. In the same time, Yahoo messenger, Skype and other
messengers work fine. I have static IP.

Same thing happened before, and I was able to solve it only by resetting the
router to factory setting. There is a number of fixes on the internet, but
this time none of them helped. This include resetting the router, restarting
the messenger, renewing the IP address (it is static), some dnsflushing
etc... I did not want to reset the router to factory setting this time.



The solution was to log into Netgear setup page (192.168.1.1 > Login etc).
Go to Firewall rules and locate on the bottom of the page section called
"Instant Messaging (IM) Ports".
Selected value was offcourse "Open IM Ports", but they were actually closed.
I selected CLOSE IM PORTS, click Apply, then select OPEN IM PORTS, click
Apply and the messenger started working again

Hope this simpe procedure helps someone else. It is by far the simplest and
worked this time for me....

Why Netgear router blocked only WLM and let Y!M and Skype running is still a
puzzle to me...