DXF saved in LibreCAD not opening in AutoCAD or TrueView

Hi,  I have a dxf file created in LibreCAD and it will not open in AutoCAD or TrueView.  

When attempting to open the files in these applications I am asked to hit "Return" but on doing that the file is not open and the application is back to as it was before.  I don't see an error message, it just does not work.

Any suggestions welcome.

Thanks, Jon