OK, sorry, I did now take the time to read all 5 pages (I'm gonna be so late for work
)
Looks like pathing is not the problem.
Is it possible that your advanced plotter settings are over-riding some setting of the printer (like "poster mode" or something) and that this is not being done on the other machines?
It seems that it works OK if you plot through another machine which means you're actually using the driver installed on that other machine as well as the CTB there, right?