SimpleXML/PHP - Can't access object

Question

$tmp2 = '<?xml version="1.0"?><RWResponse><RESPONSE><DATA><HEADER><COLUMN>interval</COLUMN><COLUMN>name</COLUMN></HEADER></DATA></RESPONSE></RWResponse>';
$xml = simplexml_load_string($tmp2);
echo $xml->RESPONSE->DATA->HEADER->COLUMN[0];

The above won't output anything, even though a var_dump is sucessful:

object(SimpleXMLElement)#2 (1) {
  ["RESPONSE"]=>
  object(SimpleXMLElement)#3 (1) {
    ["DATA"]=>
    object(SimpleXMLElement)#4 (1) {
      ["HEADER"]=>
      object(SimpleXMLElement)#5 (1) {
        ["COLUMN"]=>
        array(2) {
          [0]=>
          string(8) "interval"
          [1]=>
          string(13) "creative_name"
        }
      }
    }
  }
}

Thanks

Answer 1

This is because SimpleXML requires exact typecasting or you'll get riddiculous things happening like this - var_dump will output what you want, echo won't. You always need to do this, there are even worse bugs, like echo ceil($simplexml->someNumber) will output 7 if the number is for example 7.85 and so on.
Try instead:

echo (string)$xml->RESPONSE->DATA->HEADER->COLUMN[0];

Answer 2

The XML input is valid, I suppose the problem is with your PHP setup (old or buggy version). This is the output on my machine (PHP 5.3.8):

$tmp2 = '<?xml version="1.0"?><RWResponse><RESPONSE><DATA><HEADER><COLUMN>interval</COLUMN><COLUMN>name</COLUMN></HEADER></DATA></RESPONSE></RWResponse>';
$xml = new SimpleXMLElement($tmp2);
var_dump($xml);

// output:
object(SimpleXMLElement)#1 (1) {
  ["RESPONSE"]=>
  object(SimpleXMLElement)#2 (1) {
    ["DATA"]=>
    object(SimpleXMLElement)#3 (1) {
      ["HEADER"]=>
      object(SimpleXMLElement)#4 (1) {
        ["COLUMN"]=>
        array(2) {
          [0]=>
          string(8) "interval"
          [1]=>
          string(4) "name"
        }
      }
    }
  }
}

EDIT after update of question:

This really must be your PHP version, this is the output on my machine again:

$tmp2 = '<?xml version="1.0"?><RWResponse><RESPONSE><DATA><HEADER><COLUMN>interval</COLUMN><COLUMN>name</COLUMN></HEADER></DATA></RESPONSE></RWResponse>';
$xml = simplexml_load_string($tmp2);
echo $xml->RESPONSE->DATA->HEADER->COLUMN[0];

// output:
interval