title: Theme 'Default' cannot be found in the application
body: <p>I have the error:</p>
  <pre><code>Theme 'Default' cannot be found in the application or global theme directories
  Stack Trace: 
  [HttpException (0x80004005): Theme 'Default' cannot be found in the application or global theme directories.]
     System.Web.Compilation.ThemeDirectoryCompiler.GetThemeBuildResultType(String themeName) +920
     System.Web.Compilation.ThemeDirectoryCompiler.GetThemeBuildResultType(HttpContext context, String themeName) +73
     System.Web.UI.Page.InitializeThemes() +8699455
     System.Web.UI.Page.PerformPreInit() +38
     System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +282
  </code></pre>
  <p>My problem is, I never changed the Theme.
  I get this error just sometimes, in different pages. I don't know if this is a bug in one of the software ( EpiServer 6, IIS, Windows Server) or if I have a problem the Server's HDD.</p>
  <p>Some one have a idea about this problem.
  I know this is a trick questions, but I have no idea about this issue.</p>
  <p><img src="https://i.stack.imgur.com/jqoPa.png" alt="enter image description here" /></p>