I'm finding CodeIgniter a little frustrating right now. I really wanted to use an MVC tool, but CI is not playing well with IIS. Also, the documentation really isn't that great, even for an open-source project.
Alas, like most PHP projects it just wasn't designed or tested with IIS in mind. Fortunately I'm discovering this relatively early in the project, but I'm a little frustrated that some of these things are coming up now.
I think given the choice, since the IIS setup was decided for me before, I might have push ASP.NET Forms (vs MVC) instead. Something I'll keep in mind for next time.
Of course, CodeIgniter does work much better on my local Apache development environment. I don't want to come down too hard on it. I'm just not impressed with how it works on IIS.