Error on Method Call

I changed my xmlrpc hook to be more verbose:

function remotehello_xmlrpc() {
	$methods = array();
	$methods[] = array(
		'remoteHello.hello', // External method name.
		'xmls_remotehello_hello', // PHP function to run.
		array('string', 'string'), // The return value's type,
		// then any parameter types.
		t('Greets XML-RPC clients by name.') // Description.
	);
	return $methods;
}

Now when I call my method with a single string argument using the "Call method" page of xmlrpctester I get a message that says "Error: H" (see attached image).

I haven't defined a error H in my XML-RPC module. Is this generated by generated by xmlrpctester? I have the Devel module installed and enabled. Are there other modules I need to have?