I could be the firewall, but at the moment my own hunch is that something about the PHP on your IIS server is preventing the correct parsing of the Hot Potatoes XML source files (the "jcw" and "jmt" files), so that the HotPot module thinks this quiz is empty, i.e. has no questions.
The only way to verify for sure what is going on is to trace the execution of the PHP scripts (by inserting "print" statements to show what is going on as the scripts execute). You could maybe find a programmer to do it from within your intranet, or if you can find a way to make the server accessible to me, I would just love to investigate myself.
all the best