How to prevent IE7 file download popup blocker showing up in ASP.NET App

I have an application in .NET that allows user to download document (.rtf) by clicking a downlaod button, then a save/open dialogue opens. It works in IE6, and 8 that ways. However, in IE7, when clicking the button, a popup blocker shows at top of the web page, and user has to click the blocker, and click the dowload file menu to download the file. Once I click the blocker and the download menu within it, the blocker will NOT show up again. However, if I close IE7 windows, and start the download process again, the blocker repeat.

How to prevent IE7 file download popup blocker shows up in ASP.NET App on programming side, if possible, as opposed to make settings in IE.

It seems to do with HTTP header, or content type? Ideal solution would be that the blocker never shows up in IE7 as in other browser.

It happens even in localhost. Interestingly, the blocker does NOT shows up when clicking HTML archor link to download other files.

The message on the blocker is below:

To help protect your security, Internet Explorer blocked this site from downloading file to your computer. Click here for开发者_如何学JAVA options. Download File ...

After investigation, what happens is that before sending an url request for a file download, a put operation is sent to server (to save the change before file download), which triggers IE7 security blocker. I would like to know any workaround, and the reason if possible.

http://support.microsoft.com/kb/937409, http://technet.microsoft.com/en-us/library/cc875817.aspx