Today I solved a little, but annoying problem. It's about the problem of showing the pdf-icon after the PDF IFilter was installed on WSS 3.0 environment.
The problem was that when a user opened a document library with one or more pdf-documents in it, a login promt was shown. This was very annoying, because even when he entered his credentials again, it still continues to show the login prompt.
After cancelling this login prompt, it seems that the PDF icon was not shown.
After searching the internet, I saw some tips (like custom security settings in IE), but that didn't work out. Even a iisreset, which worked for a while, didn't do the trick.
The actual problem was the security on file level. The pdf icon file on the 12-hive\Template\Images\ had some troubles with the file security. I just opened another image from that directory, and made sure that the security permissions of the PDF icon file were identical with the other file. After fixing this, the problem with the login prompt was solved.