title: Limitations of InstallScript "Is(FILE_EXISTS, filename)"?
body: <p>My InstallScript 2014 project installs our application on a desktop PC or an embedded PC that controls an industrial instrument. The only way to know the difference is the presence of a unique USB device driver on the embedded PC that is used to enable the instrument front panel - there is obviously no front panel on the desktop.</p>
  
  <p>The InstallScript code says</p>
  
  <pre><code>if (IS(FILE_EXISTS, "c:\\windows\\system32\\mydriver.sys")) then
      do instrument stuff
  else
      do desktop stuff
  endif;
  </code></pre>
  
  <p>The file is present on the instrument hard disk in the windows\system32 folder, yet the IS function <em>always</em> returns false. </p>
  
  <p>I don't understand why this would be failing. The installer itself is running with elevated privilege, but examining the contents of Win\Sys32 does not require any special permissions - I can see the file using Windows Explorer.</p>
  
  <p>What am I missing? </p>