Due to secure by default design philosophy, IIS in Windows Server 2003 SP1 doesn’t allow unrecognized MIME types to be served. Clickonce (that ships with VS 2005) needs few new MIME types to be mapped. If this is not done, after you deploy a ClickOnce application from VS 2005, though it gets deployed successfully the application doesn’t run in the clients. To fix this the following MIME types need to added in the deployment IIS server:
FileExtention : MIME Type
.application : application/x-ms-application .manifest : application/x-ms-manifest .deploy : application/octet-stream
More information is available from these Microsoft websites: MSDN Library, Microsoft Forums.