Index: services.module
===================================================================
--- services.module	(revision 86)
+++ services.module	(working copy)
@@ -256,7 +256,7 @@
   $hash_parameters = array();
   foreach ($method['#args'] as $key => $arg) {
     if (!$arg['#optional']) {
-      if (!is_numeric($args[$key]) and empty($args[$key])) {
+      if (!is_numeric($args[$key]) and !is_array($args[$key]) and empty($args[$key])) {
         return services_error(t('Missing required arguments.'));
       }
     }