If you have dwgfiles saved by Acad 2013 (AC1027), the dwg_preview control will not show these preview in Acad and Bricscad.
Which version of OpenDCL are you using?
Sorry, for my late Reply,
I used the latest release 8.0.0.8
Can you attach a simple sample .dwg file that I can use to reproduce the problem? Which version of AutoCAD or Bricscad?