How to handle error messages in Infopath form, when a List item add event is cancelled by a Sharepoint Event Receiver? I receive an error which isn't user friendly, I would like to display a user friendly message which provides the reason why the user action was cancelled (this information is provided by the event receiver).
It's not possible to send message from event receiver to InfoPath. But you can send email to user.
Instead of using SharePoint Event Receiver, write a Custom Web Service.. Call that service from InfoPath form, you will have the option to communicate between InfoPath form and Service (SharePoint in short)..