Network share access denied / The “Make it work now plz” strategy

The next installment in my saga of doom is here! I feel as if I'm being dragged into this bureaucratic oblivion a little more each day.

Today's question's context:

My boss ordered me to make a network share so that the accountant can still use the accounting program, while the program will be on his hard drive, since the program isn't accessible no more on the now dead, buried, and mourned server.

Using a luckily uncorrupted backup, he successfully started the program. Here's where I come in, trying to share it. I ran into a problem, namely that the user cannot connect to the share.

"Multiple connections to a server or shared resource by the same user, using
more than one user name are not allowed. Disconnect all previous connections
to the server or shared resource and try again", the error told me then.

I singled it down to the boss' machine being picky, as I cannot connect to the share either from my Ubuntu netbook. I also tried creating a local account on the boss' machine, and activated the Guest account.

Both the accountant's and the boss' machines run under WinXPx64.

Any insight, tip, hint, or explosives thingie would be dearly appreciated.

Edit: I did check the share's configuration when I first shared it. "Everyone" and a local user account have both read and write permission on the share. The other connection settings (within the share) are set to be as permissive as possible, to make sure that I have the least possible problems setting it up, as I'm supposed to do it as fast as I can.

Edit revisited: It might be interesting to note that both computers are on a boat domain, and that I can't take them off from the domain to the Workgroup, lest I will break other stuff that is already working. Also, the domain controller (the ONLY one) is dead, and shares are working on other drives on the network, ie: a coworker in the same office as I have shared something over the network successfully.