Index: uc_order.module
===================================================================
--- uc_order.module	(revision 2172)
+++ uc_order.module	(working copy)
@@ -1454,8 +1454,10 @@
 
   foreach (module_list() as $module) {
     $function = $module .'_order';
-    // $order must be passed by reference.
-    if (function_exists($function) && ($value = $function('total', $order, NULL))) {
+    // $order must be passed by reference. Since hook_order() may be unknowingly 
+    // implemented (see date_order() in date_api.module), we verify the results 
+    // are numeric before continuing.
+    if (function_exists($function) && ($value = $function('total', $order, NULL)) && is_numeric($value)) {
       $total += $value;
     }
   }