We have been working with Autocad Civil 3D 2012, however our company still has various projects that were created using LDT 2009. Once in a while a file will accidentaly get saved as a 2012 file. We use the 'export' (_AecExportToAutoCAD2007) function so save it down to an earlier version, however, when the file is saved as 2012 it becomes corrupted and the export function does not work. What we have had to do is create a new file and copy all the line work over to a new drawing to be able to export it out. What can be the cause for a file to become corrupt when it is opened using C3D 2012?
That is a million dollar question as it is almost impossible to tell what made the drawing (and any file for that matter) corrupted. It can range from having bad sectors on a hard drive to some of the drawing’s recent crashes, corrupted blocks, blocks from different programs-versions, bad references, just to name a few. Moving drawing from different applications in my opinion is not a very good practice but I understand the need for it. When in need, I would recommend saving a copy of the drawing and then begin conversion. In case something bad happens you can always go back.
So in your case I would try to open it with Civil 3D 2012, then WBLOCK it and insert it into acad.dwt. Once you have new file see if you can run ExportToAutoCAD command.
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