Cannot assign the task ' ' because does not recognize one or more of the users that the task was assigned to. The task was ...

<0w> - Cannot assign the task '<1w>' because <3w> does not recognize one or more of the users that the task was assigned to. The task was moved to your Local Failures folder. Either modify the task to be assigned to a valid user or contact your site administrator to expand the site's member's list. If you need assistance troubleshooting items in your Local Failures folder, a Help topic is available at the following address: http://go.microsoft.com/fwlink/?LinkId=70300. For details, see the log file <2w>.