Parse error: syntax error, unexpected '[', expecting ')' [duplicate]
You can't have a php 5.4.3 and a 5.2.17 with a single WAMP installation, but from your error message, i think you are using the older one.
I guess, you are working with SimplXML. In this case, you should not use that line, anyway:
$media = $dc->thumbnail[0]['url'];
Note: $simpleXMLElement->childrenNodeListByName
& $simpleXMLElement['attributeValueByName']