Phil,
Not sure I can be of any help....
I have seen a similar slatted image result from a defective Meade DSI many years ago. You could see the "gaps" clearly in the histogram.
It appeared that the 8 bit signal was corrupt....
May be something similar with your ST2000XM?
Have you had this particular camera working under Maxim before??
What about downloading a trial version of AstroArt and see if it still happens?
AA6 seems to use the Version 5.2 SBIG drivers....
http://www.msb-astroart.com/ccd_en.htm