SharePoint 2010 Email Workflow Error – The user does not exist or is not unique.

I started working on SharePoint 2010 as we have moved to Office 365 environment. The migration of all my customizations have to move on to Cloud now.

Upon working on an email workflow, where in, a notification should be sent to people (one or more) who are assigned to a particular task. This was working on our on-premise environment, but stopped working when I moved it to SharePoint Cloud. Following was the error message:

The form cannot be submitted. The user does not exist or is not unique.

An entry has been added to the Windows event log of the server.  Log ID:5567

Correlation ID:026e0140-cb14-4b2e-95be-947ca2a3f86f

Upon checking all trivial settings to all custom coding, I found this article on web: People picker issue with Allow Multiple.

Let me brief the issue: SharePoint Cloud list does not get updated after you import the form template onto your Infopath 2010 and do any modifications to it on Infopath 2010.

Ideally, I should have first changed the field settings on SharePoint List settings first and then I should have imported the template onto my Infopath for further coding or modifications.

Thanks to the user (Anson Hidajat) for this crucial information. It saved me literally at least one man day’s effort.