为什么在Visual Studio 2010中禁用“使用自定义服务器”选项？

I have DotnetNuke loaded in Visual studio 2010. The 'use custom server' option under 'Start Options' is disabled. Why is it disabled? What does 'Use Default Web server' default to? How do I change what the default is? In earlier versions of VS i was able to switch between IIS and the internal web server (Cassini). Now it's more confusing in VS 2010!I have DotnetNuke loaded in Visual studio 2010.