PC's can see "Server" but says invalid user/pass

Hi guys...

I'm really stuck on this one.

I have a site that I manage with 8 computers. The software that runs on these PC's relies on a network path from the "Server". It's essentially Windows XP home. Everything is shared and I got a phone call today saying it's asking for a User/Password by one of the users.

So, I tried using the accounts on the server to login with the clients over the network. No luck. Says invalid username/pass. Tried both Admin account/pass and ordinary User.

2 out machines out of the lot are Win7 but never had an issue before connecting. Now, all the machines can't connect. But, if I go to one of the machines over the network on the server, I can login to them just fine. Firewall is off. All set to MSHOME workgroup.

I don't know what could've changed. The machines see the shared folder but when I click to go into it, the folder just has "target.lnk" in it.

Can anyone please help with this at all??

I'm so stumped atm and it's driving me nuts. My brain is fried from hunting down the net for answers and it's late.

Thanks...