CustomErrors does not work when setting redirectMode=“ResponseRewrite”

Question

In a old site, I was changing the way that CustomErrors works by adding redirectMode=\"ResponseRewrite\" (new in 3.5 SP1):

Answer 1

It is important to note for anyone trying to do this in an MVC application that ResponseRewrite uses Server.Transfer behind the scenes. Therefore, the defaultRedirect must correspond to a legitimate file on the file system. Apparently, Server.Transfer is not compatible with MVC routes, therefore, if your error page is served by a controller action, Server.Transfer is going to look for /Error/Whatever, not find it on the file system, and return a generic 404 error page!