$re = '/Activity\s+(?<timed_out>[^\\\\n]+)/m';
$str = '"Description":"Job-2069950 Error in [InfrastructureServices/Dispatcher/Interface/MQ_InterfaceDispatcher.process/JMS Queue Requestor]\\nActivity timed out\\n\\tat com.tibco.pe.core. ';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php