I think setting the right content type header when serving the AIR file should do the trick.
The value should be: application/vnd.adobe.air-application-installer-package+zip
How you set that HTTP header will depend upon your server, I've done it on app engine by a simple: self.response.headers['Content-Type'] = "application/vnd.adobe.air-application-installer-package+zip"
Not quite sure I understand where I need to apply your suggestion.
My HTML for the link to download is quite simple:
<a href="http://www.adv.co.uk/reader3/AirReader/uat/AirReader1.29.air">Windows and Linux</a>
Is it here that I need to make the change - and how - or somewhere else in the page? The site is on a Linux server.
You'll have to make the change on your Linux server.
If it is Apache, you can create a file called .htaccess in the uat directory with the following content in it:
AddType application/vnd.adobe.air-application-installer-package+zip .air
David Tucker has instructions on how to get this done on various servers: http://archive.davidtucker.net/2008/01/08/update-your-air-mime-type/
Worked brilliantly. Thanks very much.