If you intend to change permissions on IIS related directories, you must grant the anonymous user, IUSR_, the following:

  Directory Permissions

  Inetpub\Wwwroot

READ (RX)

  %SystemRoot%

READ (RX)

  %SystemRoot%\System32

READ (RX)

  %SystemRoot%\System32\Inetsrv

READ (RX)

  %SystemRoot%\System32\Inetsrv\Asp (and all subdirectories)

READ (RX)

  \Program Files\Common Files (and all subdirectories)          

READ (RX)