PHP XML validation with XSD

I need to validate some xml-files with xsd files in a php application. The problem I'm having is when I use domdocument or xmlreader, I keep getting a blank page (ERR_EMPTY_RESPONSE) when executing schema validation. I get no errors at all.

$reader = new XMLReader();
$reader->open("../xml/testxml.xml");
echo $reader->setSchema("../xml/validation.xsd") ? 'valid' : 'invalid';

$doc = new DOMDocument();
$doc->load("../xml/testxml.xml");
echo $doc->schemaValidate("../xml/validation.xsd") ? 'valid' : 'invalid';

Both files & paths of the xml/xsd exists. The php version is 5.3.1 & libxml2 version is 2.7.3 and I'm working in an OSX environment.