In IIS, you run into an interesting situation when you need to access another resource off of the IIS server and certain fairly common situations occur. When using Integrated Security, anonymous access is disabled, and impersonation is turned on, a security measure kicks in and doesn't allow your site to access resources on any network servers. This includes access to a UNC path directly from IIS or SQL Server using Windows authentication.
I've written a couple times about what configuration changes cause AppDomain recycles. Most recently how the ASP.NET tab causes a server-wide AppDomain recycle, and previously about changes in ASP.NET 2.0.
This blog post was a long time coming and fortunately doesn't apply to IIS7, but I thought I would finally take a few minutes and cover this shortcoming with the ASPNET tab that ASP.NET 2.0 introduced into IIS 6 and IIS 5.