4.2. We're sorry, the Interchange server is unavailable...
(The following assumes that you were able to start the Interchange server.)
This could be almost anything, but with a properly configured Interchange it is almost undoubtedly due to your cgi-bin and/or your Interchange directory being located on a different filesystem than the actua 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 Interchange server. Please read the documentation that covers this in detail.
You can run in INET mode with the tlink link program to prevent those problems.