One host suddenly quit working (kind of)

[mewnlite]

I have 4 computers at the phone company all running UltraVNC hosts with different port settings. Our TP-Link router is set to route incoming requests to the proper machine. I access all of them regularly from home. They have all worked flawlessly for at least a year. However, two days ago, one of them became inaccessible. I have checked all the settings and even reinstalled UVNC on that machine. I have checked the router settings. Nothing has changed. We use a security program called Secureit which we get through our ISP on three of the four machines including the one that became inaccessible. What is really strange is that the machine CAN be accessed from any of the other local machines by using the local IP addresses. The only thing that is different about that machine is that it is running version 10.8.2 whereas the other three are all running 10.5.6. I've tried disabling the security and the Windows firewall. I've rebooted the router and of course the computer itself several times. Right now, from home, I can only access it through one of the other computers which is slow and cumbersome.
Does anyone have an idea what might be going on? Was there a windows update that might have affected vs 10.8.2 and not the older version? Needless to say, it is the computer I need access to the most, since it is the one that controls all the telephone equipment.
I forgot to mention all the computers are running XP Pro SP3.
Thanks for any suggestions!

[mewnlite]

I shut down UltraVNC on the affected machine and started up Show My PC. I generated a number, wrote it down, went home and tried it. It worked. So how can ShowMyPC get through to it and UVNC can't? As I mentioned before, it worked faithfully up until about three days ago. I totally uninstalled UltraVNC 10.8.2 again today. I removed all folders and registry entries that had anything to do with it and then reinstalled it. It still doesn't work from home. The only thing I can think of now is to uninstall it again and install 10.5.6 which is the version on the other machines which are still accessible. My viewer is 10.8.2.
Any ideas appreciated!

[mewnlite]

For reasons unknown last night the problem went away. I can now access the machine and have logged in and out several times. I have made no changes on anything at home.
Would have posted this last night, bu the forum was broke...