Article ID: 2503931 - View products that this article applies to.
Consider the following scenario:
This issue occurs because the msOnline-UserPrincipalName attribute is a reserved attribute in the Active Directory domain schema.
To resolve this issue, apply the following hotfix:
(http://support.microsoft.com/kb/2475878/ )Description of the SharePoint Server 2010 Cumulative Update Server Hotfix Package (MOSS server-package): March 3, 2011
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.