If you are trying to open an AutoCAD DXF file from the late 80s or 90s and get things like "Unknown error" in Illustrator or other software, just get a blank page in AutoCAD or a generic "failed" message, try this.
Open the DXF file in your favorite text editor.
Near the top, maybe line 6 or so, find $ACADVER.
Under that, you should see 1, and then the DXF drawing database version number.
If you see something outside of the official list (http://images.autodesk.com/adsk/files/autocad_2012_pdf_dxf-reference_enu.pdf), it probably won't work.
Our issue was that it said CGT1.1, looking like this:
$ACADVER
1
CGT1.1
So we changed it to:
$ACADVER
1
AC1006
CGT1.1 is CorelDRAW version 1.11, the first version to include DXF support, from early 1990, and so AC1006 was the most recent version of AutoCAD at the time.
Save the file with the new value, and it should open in Illustrator.
The full list of DWG tags can be found on wikipedia: https://en.wikipedia.org/wiki/AutoCAD_version_history
The CorelDraw versions: https://en.wikipedia.org/wiki/CorelDRAW#Features_by_version
For most success, match up your version (CGT1.1, etc.), find the release date, and choose the AC version released before then. Probably 1-2 years before.
The most likely to be relevant for fixing your issue:
- AC1006 = R10; - 1988, October
- AC1009 = R11 and R12; - 1990, October
- AC1012 = R13; - 1994, November
- AC1014 = R14; - 1997, February
- AC1015 = AutoCAD 2000; - 1999, March
- AC1018 = AutoCAD 2004; - 2003, March
- AC1021 = AutoCAD 2007; - 2006, March
- AC1024 = AutoCAD 2010