ClickOnce is a great technology, but it seems that documentation is a bit scarce... In particular, like all web-based technologies, it requires some obscure configuration. The web may be great in some ways, but it does often require that you have a lot of arcane knowledge to do even the simplest thing...

This forum thread covers the little-documented fact that for IIS 6.0 the web server serving up a ClickOnce application needs to map the .application, .manifest and .deploy file types in IIS as follows:

.application -> application/x-ms-application
.manifest -> application/x-ms-application
.deploy -> application/octet-stream

While this may be documented somewhere, it seems quite hard to find. Thus I'm blogging it. If a few people blog the answers to common questions than at least google finds them for people :)