Dreamweaver MX 2004 Security Warning

I have been using MX 2004 blissfully for several years but this week it has opened and been immediately overlain by a Dreamweaver MX 2004 Security Warning saying that the named file (swflash.cab) does not have a valid digital signature.

This link carries a screen shot: http://sspx.co.uk/swflash.cab.png

I am not trying to install any new software.

I have clicked on the "Unknown Publisher" link and successfully installed Adobe's current certificate.

I have clicked on "Install" and been told that a download of Adobe Flash Player could not take place as I am (it says) possibly not connected to the Internet. I am.  I located a free-standing Adobe download and successfully installed that so I am now on Shockwave Flash 26.0.0.131.

I have force quit and restarted Firefox (latest version).

I have restarted my computer (iMac running Sierra and Parallels with XP Professional).

And still I get this Security Warning.

If I click on the "Shut down" cross in its top right hand corner it shuts down and I am able to run DW with no problem at all.

It is simply that this Security Warning is a nuisance and an unexplained source of stress.

Could a kind person out there please tell me how to rid me of this troublesome display?