Problems reading a test chart: "seem to have read strop pass X"

[Jean-Michel Pouré - GOOZE <jmpoure gooze eu>]

Dear all,

I am using the Colormonki (black) to read a print test chart in order to
calibrate the printer.

It seems like I am holding the ColorMonki as explained on Argyll web
site:

***

For the ColorMunki with the default chart, the patches are the same
width as the silver portion of body (white version), or the textured
portion of the body (black version). Place aperture of the the
instrument (located at its center) in the white space ahead of the first
patch, and then press and hold the instruments button. When you hear a
beep from the computer, you can then move the instrument steadily over
the patches, releasing the button after the instrument is past the last
patch. Moving the instrument too fast or changing speeds may cause a
mis-read, or a scan with few samples read per patch. For the high
density ColorMunki chart (printtarg -h), the patches are arranged so
that three rows are exactly the width of the  body of the instrument. If
you are careful you can use this to guide the center of the instrument
over each row, or you may prefer to use something like a plastic ruler
to help guide the instrument.

***

So everytime I read the chart, it answers:
"Ready to read strip pass A" and then "Seem to have read stip pass G"

This goes on and on for every strip, but with different letters.
Trying to re-read the line will not change anything.

Any idea?

Kind regards,
Jean-Michel