The below all assume you were able to start the MiniVend server.
This could be almost anything, but with a properly configured MiniVend it is almost undoubtedly due to your CGI-BIN and/or your MiniVend directory being located on a different filesystem than the actual machine that is executing the program. VLINK uses UNIX-domain sockets, which don't work on NFS-mounted filesystems.
Iserver.com and other systems which use chroot HTTP servers require quite a bit of extra configuration to get going.
If you have not been careful to set permissions properly when running in VLINK/UNIX mode, the link CGI will not be able to communicate with the MiniVend server. Please read the documentation, which covers this in detail.
You can run in
INET mode with the tlink link program to prevent those problems.