I recently ran into some frustrating problems doing something that ought to be really simple: setting up a directory on IIS so that the files could be downloaded with a HTTP GET. Some files would work fine; others would get a 404 error (NOT FOUND).

Here’s a checklist of possible configuration problems:

• Right-click on the top IIS Manager node, select Properties and press the MIME Types button. Make sure a MIME type is defined for the file extension.
• Click the Web Service Extensions node and make sure there is no web service extension defined for that particular file type. If there is IIS will try to pass the file to it rather than download the file.
• If the file is executable (.dll, .exe, etc.) bring up Properties for the web application, select the Home Directory tab and make sure Execute Permissions is set to “Scripts only”. (NOT to “Scripts and Executables”.)