Right, but why don't you use TCP/IP between the cash register and the ECR server ? (Perhaps the cash register is not PC based ?)
Yes, they are standalone(not PC based).

Which VFP restrictions ?
It is not possible to use Method and Event with the same name.

You're talking about Listen function and the backlog (=5) parameter (which limit the usage of Ms Winsock OCX)

int listen(
SOCKET s,
int backlog
);
Yes, including multi-instantiation of standard OCX

Fine, how could I test it ?
Send on my e-mail a message and I will reply with trial version of OCX.