Do you know if your IP address changed at that time? Sometimes these messages happen because someone was infected, and they used to have the IP address you have now. I used to have this problem often when I had a dialup connection that gave me a different IP every time. Sometimes networks can have wildcard bans, where they might have banned a range of IP near yours. Hopefully the network has a website with a method of contact once the problem is fixed.
Have you tried connecting to different networks to see if you are also banned there too?
