Description

Duplicate submissions or emails can be sent when using Web Forms For Marketers (WFFM) 9.0.1 - 9.0.2 on Content Delivery instances. The issue is caused by WFFM misconfiguration. The errors similar to the following can be found in log records:

ERROR Exception while handling event Sitecore.Form.Core.WffmActionEvent
Exception: System.AggregateException
Message: One or more exceptions occurred while processing the subscribers to the 'wffm:action:remote' event.
Source: Sitecore.Kernel
   at Sitecore.Events.Event.EventSubscribers.RaiseEvent(String eventName, Object[] parameters, EventResult result)
   at Sitecore.Events.Event.RaiseEvent(String eventName, Object[] parameters)
   at Sitecore.Eventing.Subscription`1.Invoke(Object instance, EventContext context)
   at Sitecore.Eventing.EventProvider.RaiseEvent(Object event, Type eventType, EventContext context)

ERROR One or more exceptions occurred while processing the subscribers to the 'item:saved:remote' event.
Exception[1]: System.InvalidOperationException 
Message[1]: Invalid event arg type: Sitecore.Data.Events.ItemSavedRemoteEventArgs. Expected: SitecoreEventArgs 
Source[1]: Sitecore.Kernel 
   at Sitecore.Events.Event.ExtractParameters(EventArgs args)
   at Sitecore.Events.Event.ExtractParameter(EventArgs args, Int32 index)
   at Sitecron.Events.SitecronSavedHandler.OnItemSaved(Object sender, EventArgs args)
   at Sitecore.Events.Event.EventSubscribers.RaiseEvent(String eventName, Object[] parameters, EventResult result) 

Solution

To resolve the issue, rename the \App_Config\Modules\Wffm\Sitecore.Forms.CD.config file so that it becomes the last one in that folder (for example, to "z.Sitecore.Forms.CD.config").