Saving to DXF file does not work

Apologies if this issue has already been posted on here (haven't read ALL of the posts).   I've done the install etc., and it 'appears' to be saving the file as a DXF, but the company that I'm sending the file to is not able to open it.  When I check the type of file that it is {right mouse on file name for example}, it gives the file type extension as: file   NOT .dxf as I would have expected.  I also notice in: window > preferences > extension that althought the skp_to_dxf box is ticked (Checked), the tick appears kind of greyed out.  It IS ticked, but not as solidly as the others.  Unfortunately I'm in a bit of a hurry to send this file for cutting, and although I just downloaded Autocad LT2016 (and I am reasonably familiar with Autocad), I'm having difficulties learning how to 'drive' this version of Autocad, and I can't spare any more time on it at the moment.  Please help.  Please also reply to:

  as I am not a member of this forum and I'm not sure how to get back here.  Regards Mark

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DXF plugin

Hi Mark - I have sent you an email about your issue.

Nathan