I can't find an reference to the source of this error. I did find some similar error messages stating that it requires a re-install of autocad, however nothing relating to this one exactly. I can open other dwg's fine, but on this one file both the .dwg and the .bak files are corrupted. Any ideas Autodesk?
I am using Autocad Mechanical 2012
Have you updated service pack 1 of Autocad Mechanical 2012?
Also, please also try to RECOVER the drawing to fix any errors.
If it doesn't work, could you please send me the drawing file to email@example.com?