This issue occurs because the light version of Outlook Web App uses a Lightweight Directory Access Protocol (LDAP) query that references the showInAddressbook attribute to retrieve the user’s information from the global catalog server. However, the user does not have the showInAddressbook attribute. Therefore, a MissingArgumentException exception is thrown.
To resolve this issue, install the update rollup that is described in the following article in the Microsoft Knowledge Base:
2685289 Description of Update Rollup 3 for Exchange Server 2010 Service Pack 2
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.