I'm working on a site that is quite strange in it's set up, but it is what it is....
....Anyway, a page on site A has an iframe opening a page on site B. The IFrame displays info about a file stored outside the website of Site B but in the c:\root of the site B server.
The page on site B has a button which uses a filestream to open, and present the file dialog box to the user.
Whn accessing the site B page directly the file is served successfully, when pressed within the iframe, nowt happens.
My client doesnt have the problem, I think what has happened is that the test site I was looking at didnt have the files on the server, although had a record for them in the database.