Hello Steve,
Having just read your post I can now narrow down the issue a little further…
The two browsers I tried which didn't work are on a machine different to the one browser on which it did work. I have now tried using google chrome (v8.0.552.215) on the machine which was running firefox (v3.0.16 - the one which worked), and I can say that uploading files using v8.0.552.215 on that machine does work. One difference seen in the browsers on the machine which works is that, they show a different upload file popup window to the ones shown in the browsers which don't work. The popup windows which do work include the following message: 'With the latest Flash Player installed, you can upload multiple files. Download it from the Adobe Flash Player Download Center'.
Can the problem therefore be in the version of Flash which is installed on the machine whose browsers do not work?
Regards,
PM.