Like a lot of file formats, the details of the DXF format has changed over time and changes to this format is not in our control.  Accordingly, newer versions of software that export or save in DXF format may be using a newer vesion of the format. Generally this can be overcome by simply selecting to save the DXF file as an older format from your original source.

What to do if you do not have access to the original source:

 1. Try selecting DXF from the file type drop down when importing, this has sometimes overcome some DXF compatibility issues.

 2. There are some DXF/DWG conversion programs that you can download.  Try doing a web search for such programs...most of them allow you to back convert the files to older versions.