1.Trying to send a file to a web server and the server application does not have rights to write files.
2.The virtual directory does not have the "write" permission checked.
3.The virtual directory does not exist.
4.May be trying to download a file that IIS thinks is an executable file. For example .CDX files. If so, go into the virtual directory "application configuration" and delete CDX from the list.
5.Trying to send a file to a web server and the folder (path) does not exist. Check URL for missing slashes.
6.Web server requires SSL connection but client is using http.