Several things that could be causing this;
First double check from another client machine and see if you get the same error. Try substituting the IP address of the T2 machine like Link Removed (actual ip of machine)
Check the properties of the network card on the client machine, make sure that "Client for Microsoft Networks" and File and Printer Sharing for Microsoft Networks" are both checked. Select Internet Protocol Version 4 and click the properties button, click the advanced button and select the WINS tab, click the radio button that says "Enable NetBIOS over TCP/IP and OK your way back out of there, select the advanced tab and click the settings button, make sure that under the exceptions tab of the windows firewall setting dialog box that file and printer sharing is checked.
Type services.msc into the run dialog box (Windows Key + R) hit enter, check and make sure that both the server service and the workstation service are started and set to automatic as thier startup type.
Remove any type of third party application that may be acting as a supplemental firewall, Comodo, ZoneAlarm, any of many Internet Security Suites.
Microsoft recently announced that they are allowing Small Businesses (10 computers or less) to utilize their Link Removed due to 404 Error product so consider replacing your current application with that product since it seems to be a great deal more network friendly, very small footprint and resource friendly and seems to do a pretty good job. It's supported on XP Service Pack 3.
Do you have all your client machines configured to use static IP addresses?
Like T2 192.168.1.102, T3 192.168.1.103, T4 192.168.1.104, etc. If not, consider doing something similar, if you are relying on DHCP from something other than your Domain Controller hosting DHCP services (like a third party router) there maybe some lag in DNS updating its' service records regarding a particular client (hostname) and a new or different IP address, just a thought.