QTR-Quadtone RIP

Hello All;

I'm tying to get a friend started with QTR on a 2200 and OEM UC inks, 
and we've run into an odd problem. She's on a Mac-Intel with OS 10.4, 
using QTR 2.42.
The problem: she's getting PRINTED vertical faint minus-density lines 
in the 95%-100% zone. The lines are diffused, about 1/8" wide, and 
about 1.4" apart.  These are NOT pizza-wheel or roller marks, you can 
watch them being printed as the paper goes through. We've printed the 
same black field with both QTR and the Epson driver, and it ONLY shows 
up with QTR, there's no trace of it with the Epson driver.  Can anyone 
help with this? 

Thanks.

Steven Karafyllakis