Intermittent User Lookup error after Pause

Aug 4, 2011 at 5:33 PM

We have a workflow that, after a 7-day pause, uses the "Lookup site user property" action to lookup two user properties (Title and EMail) and stores them in workflow variables that are later used with a "Send Email Extended" action.

This workflow is running on a list with 3000+ items. After the 7-day pause, the workflow is erroring out for most (BUT NOT ALL) of the 3000+ items. The error is:

System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
Parameter name: User not found

System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
Parameter name: User not found.

System.ArgumentException: The parameter 'addresses' cannot be an empty string.
Parameter name: addresses
   at System.Net.Mail.MailAddressCollection.Add(String addresses)
   at DP.Sharepoint.Workflow.Common.PopulateMailAddressCollection(MailAddressColl

We're wondering why this is happening, but not to all of the item lines. And, if this has to do with so many items firing off at once, how would we "stagger" the grabbing of user info and sending of emails with some reasonable delay between so that such intermittent errors won't occur?