No, I'm running AutoCAD Mechanical 2007. I did try it in the 2006 version and it still worked correctly. Do you have a layer that is turned off or frozen which is not displayed or copy and paste to this site. If there is, and there is items on that layer which are in that off center space. It will cause it to appear not centered. You may want to use your drawing utilities and purge any unwanted, text, layers, blocks, etc. That may resolve your issues or use the "wblock" command, save it under a differnent name and see it that works.