title: CodeDom provider can't be located after another application deployed
body: <p>I had two web applications deployed in a site under IIS 7.5</p>
  
  <blockquote>
    <p>site.com/myApp
    site.com/anotherMyApp</p>
  </blockquote>
  
  <p>Now another devs deployed their app as root application</p>
  
  <blockquote>
    <p>site.com/</p>
  </blockquote>
  
  <p>Now when I access <code>site.com/myApp</code> or <code>/anotherMyApp</code> it throws:</p>
  
  <blockquote>
    <p>The CodeDom provider type
    "Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider,
    Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0,
    Culture=neutral, PublicKeyToken=31bf3856ad364e35" could not be
    located.</p>
  </blockquote>
  
  <p>Source error : </p>
  
  <pre><code>Line 54:   &lt;system.codedom&gt;
  Line 55:     &lt;compilers&gt;
  Line 56:       &lt;compiler language="c#;cs;csharp" extension=".cs" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:6 /nowarn:1659;1699;1701" /&gt;
  Line 57:       &lt;compiler language="vb;vbs;visualbasic;vbscript" extension=".vb" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" warningLevel="4" compilerOptions="/langversion:14 /nowarn:41008 /define:_MYTYPE=\&amp;quot;Web\&amp;quot; /optionInfer+" /&gt;
  Line 58:     &lt;/compilers&gt;
  </code></pre>
  
  <blockquote>
    <p>Source File: C:\inetpub\wwwrootprettysite\THEIR APPLICATION\web.config</p>
  </blockquote>
  
  <h2>Questions</h2>
  
  <p><strong>Why is this happening?<br>
  Why is the "source error" in <em>their application's webconfig</em> and how does it affect my application?<br>
  How do I fix my applications without breaking theirs?</strong></p>
  
  <p>To clarify : </p>
  
  <ul>
  <li>Application hierarchy is correct, their application should be<br>
  installed in root.</li>
  <li>.NET framework installed is 4.5.2</li>
  <li>Their application is using Roslyn compiler which is supplied in bin/roslyn</li>
  <li>My applications web.configs have no <code>&lt;system.codedom&gt;</code> section.</li>
  </ul>