Digital BW, The Print

Hi all, I had a strange experience today and I need some 
advice. I discovered a public art opportunity in my area with 
short notice last week. They require 5 slides of my 
prints for judging. These are B&W prints made on a 2200 with
the standard UltraChrome inks, standard Epson driver.

I'd never shot slides of prints before, but I decided to set 
up my 35mm Nikon and shoot a roll of Ektachrome 64T tungsten
balanced film. How hard could that be? I closed the vertical
blinds, taped the prints to a black matt board & hung them on 
a wall, set up a couple of tungsten photo lights (3200K) 
(not strobes) and exposed 36 slides for 1/4 second, based on 
my spotmeter reading (with some aperture-based bracketing to 
cover my bets.) No filter on the camera or in front of the 
lights.

As far as I understand, this is all standard operating procedure 
for photographing flat artwork. Though as I say, I've never done
this before.

I just picked up the slides. They were exposed correctly, but 
every one has a deep magenta cast. The prints looked nicely 
neutral to my eye when shooting. 

I could shoot another roll of slides, but I don't understand
what I ought to change. Is it possible this is a function 
of metamerism in the UC inks that only appears on color film?
(That sound ridiculous to me--I'm embarrassed to even state the
question. But there it is.) Has anyone shot slides of UC prints 
as described above and got neutral results? Or can someone guess 
from the above description what sort of dopey mistake I made?
Could the lab that processed the film have screwed them up
somehow?

Thanks for all advice,
David

ps. I know I could find a service bureau to print the slides
from a digital file, or use Scala, but I thought this would be 
both cheaper and faster. In the future, when I have more time to 
prepare, I imagined I would use Scala.