scott976 said:
I don't think you can redirect from global.asax.  You need to enable custom errors in your web config and set the default redirect.

To answer the original post in custom errors tag in your web config you can handle specific errors by doing:

<customErrors mode="On" defaultRedirect="~/AppError.aspx">
            <error statusCode="404" redirect="AppError404.aspx"/>
</customErrors>


Yes you can redirect from global.asax, ie. Server.Redirect("Error.aspx");