QTR-Quadtone RIP

I have installed and tested QTR on my own Epson 4000, and gotten
excellent results. (Mac OS 10.3.9)

However, when I tried to use QTR with our school's 4000, I get
banding. I have run nozzle checks, head cleaning cycles, and head
alignment.  I have also 
madesure that the school's machine had the latest software and
firmware.
This machiine, though, does not produce banding when printing color
images with the
Epson drivers.

Does anyone have a suggestion as to a solution to this problem?

Thanks in advance, 

Peter