John,
What you have is a Dead-Short in the 4th fitting.
It sounds to me like these lights are in Parallel, not Series.
The short is preventing any current flow to the other fittings further down the track.
If the guy keeps running the system like that he will need a new transformer.
{Message edited to add last bit}
[This message has been edited by Trumpy (edited 01-03-2005).]