I ran into an interesting issue today when working on an ASP.NET 2.0 Web Application Project that I had not heretofore seen.  Very frequently, but not 100% of the time, upon debugging my application from Visual Studio 2005 I would encounter an error message resembling "Cannot create/shadow copy 'XXX' when that file already exists." where 'XXX' is the name of some resource in my project.  I hadn't seen this error before installing SP1, leading me to believe it has something to do with that upgrade.  However, almost all of my Web Application Projects are done with IIS and not the Cassini web server - so maybe it's Cassini related.

Nonetheless, it's pretty easy to fix.  You simply have to tell ASP.NET not to shadow copy the project assemblies to the ASP.NET temporary folders file by updating your web.config with the following entry:

<configuration>
   <system.web>
      <hostingEnvironment shadowCopyBinAssemblies="false" />
   </system.web>
</configuration>

Then just restart your Cassini web server or simply right-click it and select 'Stop'.  That cleared it up for me.