Couple of days ago, I installed BlogEngine.NET on my home server's root directory. Besides being extremely impressed by BlogEngine.NET, I noticed that all of my other sub-applications started crashing. Immediately, I knew that the installation of BlogEngine.NET affected all other web applications. After short investigation, I noticed that all of my sub-applications were trying to load handlers and modules defined in BlogEngine class library. Specifically, all web applications tried to load following:

[...]
<httpModules>
      <add name="WwwSubDomainModule" type="BlogEngine.Core.Web.HttpModules.WwwSubDomainModule, BlogEngine.Core"/>
      <add name="UrlRewrite" type="BlogEngine.Core.Web.HttpModules.UrlRewrite, BlogEngine.Core"/>
      <add name="CompressionModule" type="BlogEngine.Core.Web.HttpModules.CompressionModule, BlogEngine.Core"/>
      <add name="ReferrerModule" type="BlogEngine.Core.Web.HttpModules.ReferrerModule, BlogEngine.Core"/>
      <!--The CleanPageModule below removes whitespace which makes the page load faster in IE. Enable at own risk -->
      <!--<add name="CleanPageModule" type="BlogEngine.Core.Web.HttpModules.CleanPageModule, BlogEngine.Core"/>-->
      
      <!--Remove the default ASP.NET modules we don't need--> 
      <remove name="PassportAuthentication" />
      <remove name="Profile" />
      <remove name="AnonymousIdentification" />
    </httpModules> 

    <httpHandlers>
      <add verb="*" path="file.axd" type="BlogEngine.Core.Web.HttpHandlers.FileHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="image.axd" type="BlogEngine.Core.Web.HttpHandlers.ImageHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="syndication.axd" type="BlogEngine.Core.Web.HttpHandlers.SyndicationHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="sitemap.axd" type="BlogEngine.Core.Web.HttpHandlers.SiteMap, BlogEngine.Core" validate="false"/>
      <add verb="*" path="trackback.axd" type="BlogEngine.Core.Web.HttpHandlers.TrackbackHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="pingback.axd" type="BlogEngine.Core.Web.HttpHandlers.PingbackHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="opensearch.axd" type="BlogEngine.Core.Web.HttpHandlers.OpenSearchHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="metaweblog.axd" type="BlogEngine.Core.API.MetaWeblog.MetaWeblogHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="rsd.axd" type="BlogEngine.Core.Web.HttpHandlers.RsdHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="css.axd" type="BlogEngine.Core.Web.HttpHandlers.CssHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="js.axd" type="BlogEngine.Core.Web.HttpHandlers.JavaScriptHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="rating.axd" type="BlogEngine.Core.Web.HttpHandlers.RatingHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="opml.axd" type="BlogEngine.Core.Web.HttpHandlers.OpmlHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="monster.axd" type="BlogEngine.Core.Web.HttpHandlers.MonsterHandler, BlogEngine.Core" validate="false"/>
      <add verb="*" path="blogml.axd" type="BlogEngine.Core.Web.HttpHandlers.BlogMLExportHandler, BlogEngine.Core" validate="false"/>
</httpHandlers>
[...]

At first, I was very confused that all sub-applications are loading web.config from the root application. I thought that each web application simply used the web.config from it's own virtual folder (besides machine.config). To investigate the issue, I started searching the web and after a short time I found the following article. The article explains the way IIS 6 is handling web configuration loading and inheritance. Frustrated with the result, I was determined to find solution to my problem. And then it hit me: <location> tag! With <location> tag, it is not only possible to control application security, but also selectively load parts of web.config. Actually, the accurate statement would be that <location> option allows user to control if "child" applications will inherit portions of web.config. In this way, I was able to pick and choose, which parts of web.config will be loaded in sub-applications. Following part of web.config explains everything:

[...]
<location inheritInChildApplications="false">
 
  <system.web>
    
  [...]   
 
  </system.web>
  
</location>
[...]

Adding <location> option solved my headache ...