To add to my frustrating time this week with my 1418 error when setting up Database Mirroring under SQL Server 2005. I was dogged by a continuous 'Service Unavailable' message when trying to load a ASP.NET page under IIS running under Windows 2003 R2.
Typically 'Service Unavailable' is a nice catch all message that doesn't give anything away, and so it shouldn't as hackers learn about websites by generating exceptions.
Diagnosing the real reason for the error is a case of reading the IIS error logs and looking for one of these reasons on the Microsoft 503 webpage.
Microsoft Support has support articles 823552 & 842493 covering the other reasons that cause the error.
Well I've found another reason that causes this message to appear I haven't found documented else where, hence the reason for the post.
If IIS isn't installed initially with the operating system and service pack 2 is then applied, then install IIS from the original media will cause IIS to not work and consistently throw 'Service Unavailable' when asked to build and display a page.
The answer is to re-install service pack 2 after installing IIS and 'Service Unavailable' message will disappear for that reason.
Obviously installing IIS over service pack 2 forces some kind of retrograde step to happen which the install process does not detect but this is only my assumption.
Anyway, I hope this helps solve this issue for you if you stumpy across this post which I hope Google is kind enough to put somewhere not to far from the first page. Please let me know.