I was just testing the site and ran into a problem with Flash image loading. I found that when loading a nonexistent file, Flash still reports progress info, and after reaching 100% it shows nothing.
I was completely baffled. Later I checked with Firebug and found that the image being loaded actually came back with an HTTP header of 200 status, and there was even a file there! Then it hit me — it was caused by the 404 error page I had set up in IIS.
There’s one thing to watch out for here: IIS lets you specify the 404 error page in two ways. One is a relative URL, the other is a local file. If you use the URL method, IIS returns the 404 page but sends a 200 status header with it, which is effectively a redirect. Only with the file method does IIS return a 404 status header. Remember this, remember this…