Spring.NET does not support virtual apps in IIS Express

I am running two web apps on IIS Express:

• localhost:8000/ <- Web App 1, ASP.NET Webforms
• localhost:8000/subdir <- Web App 2, ASP.NET MVC

I am using .NET Framework 4.5.2.

I am getting back a 500:

HTTP Error 500.19 - Internal Server Error
Module     IIS Web Core
Notification       BeginRequest
Error Code     0x800700b7
Config Error       There is a duplicate 'spring/context' section defined
Config File    \\?\C:\webapp\subdir\web.config
Config Source:
   12:     <sectionGroup name="spring">
   13:       <section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
   14:       <section name="objects" type="Spring.Context.Support.DefaultSectionHandler, Spring.Core"/>

Why am I getting this message?

My previous configuration worked:

• localhost:8000/ <- Web App 1
• localhost:8001/ <- Web App 2

However this is no longer accepted.