With the help of NetConsole (you're right - it's great - no more serial ports!), and some finagling of the unfamilar debug tools, and the help of people in this thread, I found out that.....drumroll.....
....I had declared a function but did not define code for it. A very basic d'oh.
Wish that kind of stuff was presented more obviously to the *basic* end user.
Anyway, thanks again to all who provided advice and assistance in this thread.