Using Robocopy to deploy sites

I want to be able to quickly deploy updates to a site that is fairly busy. For smaller sites I would just FTP the new files over the old ones. This one, however, has a few large dll’s that regularly get updated and while they are copying the site is effectively down (plus there is the hassle of making backups of them in case something goes wrong.

SoapHttpClientProtocol.ReadResponse – The request failed with HTTP status 401: Unauthorized

I have an ASP.NET (v2.0) web application that uses a reference to a SQL Server Reporting Services 208 R2 instance (using the ReportService2010.asmx service endpoint). The web application is hosted on ServerA and the Reporting Services instance is hosted on ServerB. ServerA is running Windows Server 2003 (IIS6) and ServerB is running Windows Server 2008 R2.