Help: Fatal error doing an export (Civi 4.7.4)
Line 435 in CRM/Export/BAO/Export.php that your error message is referring to says:

if (!empty(self::defaultReturnProperty($exportMode))) {


This will give an error in all PHP versions below 5.5. From the PHP manual (http://php.net/manual/en/function.empty.php):


  Prior to PHP 5.5, empty() only supports variables; anything else will
  result in a parse error


You should be able to fix this by replacing lines 435-437 in Export.php with something like

  $key = self::defaultReturnProperty($exportMode);
  if ($key) {
    $returnProperties[$key] = 1;
  }