Digital BW, The Print

Hello,
I hope some expert is able and willing to help me with the problem I
encountered, cause it drives me nuts and I can't go on with my work if
I don't get it right.

CONFIGURATION:
Epson 1160
MIS UT-FS inkset (quadtone, monochrome)
Windows XP

PROBLEMS:
Today, immediately after I refilled the carts, the ink in the
Y-position printed far too dark. I could even see it in the printed
nozzle check pattern. While it should be the lightest of the 4 inks,
it prints even darker then the ink in the M-position.
And: there are strange dark and light lines to the left margin of a
printed swatch (which is not banding), not once but every time.
(See the picture at http://members.chello.nl/iwesdorp/problem/yellow.jpg)

First I thought I had used the wrong ink for filling the Y in the
cart, but that was not the case. And I tried all kinds of things:
making lots of purge/flush prints, resetting the printer, taking out
the carts etc. But to no avail.

Does anyone know a remedy?

Thank you so much.

Igor
Amsterdam