I was having trouble getting an ASP.NET 2.0 site up and running today on a (new to me) server.  I could browse static content from the site, but any ASPX pages would return a 404 error.   At first I thought I was mistyping the URL, then I thought that ASP.NET just wasn't registered so I ran the aspnet_regiis.exe utility, but still no dice. 

I played around with all kinds of settings until I find that ASP.NET was completely disabled on the server under Web Service Extensions.  For ASP.NET to work the WSE for ASP.NET must be set to allowed!  I have no idea why it was disabled, but it was.  Argh!