Windows can do that if I don't have an account there. That and XP has a limited number of connections. 7 machines can be a few too many.
That's just two issues and I can't see any note where you dealt with account issues.
In short if I'm logged on as will on my other PC I can see that message from XP as I don't have an account there. It won't allow me on. Yes you could enable the Guest account but there goes the security.
Bob
On my network I have two 8.1 pc's, two 7 pc's, and have a dual-boot with Linux situation. If I VNC into the XP machine and open My Network, I can open and read/write/create/delete folders on every other machine, including the Linux. However, none of the other pc's can access the XP. Every machine gets the "You Don't have permission, contact your network administrator" error message.
I found a Windows help page, that shows what ports need to be open on the XP machine, that didn't work, I have tried a couple of other networking software downloads, VNC works great, but it is the only thing, and I have been researching this for over a month. I found instructions on how to configure both 7 and 8.1, that didn't work either.
The whole thing is I use the XP machine to run educational software for my son, stream Netflix to the living room tv, and it is the only tower I have, everything else is laptops, and I want to install a large HDD (at least 1TB), so I can use it for a backup server for the rest of the machines.The educational software only works on Windows, or I would just install Linux, Since it's the only the tower, and only one not being moved around, so it's the only one I could add another HDD to. If one of the laptop's was stationary, I could use a usb drive, but I can't count on a laptop to be in a certain place at a certain time.
Can someone give me some tips that might work, I found one program that I installed on the XP, that will "pull" files from the other pc's like a server, but I don't think it's real reliable, so I would rather do something else. If I can't get things set up so I can access the XP machine, I guess I can install Linux, and their educational software, which I've looked at and wasn't impressed. I've paid a lot of money for these DVD's we have now, so I hate to throw them away by installing Linux over the XP, and I don't think I can set a timer so the computer will reboot into the other OS.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic