An error occurs when a user whose mailbox is hidden from the Exchange address list tries to open the Scheduling Assistant tab by using the light version of Outlook Web App

Applies to: Exchange Server 2010 EnterpriseExchange Server 2010 Standard


Consider the following scenario:
  • A mailbox user is hidden from the global address list in a Microsoft Exchange Server 2010 environment.
  • The user accesses the mailbox by using the light version of Outlook Web App.
  • The user creates an appointment or a meeting request and then clicks the Scheduling Assistant tab.
In this scenario, the user receives the following error message:
An unexpected error occurred and your request couldn’t be handled.

Url: URL
User host address: Host Address
User: User
EX Address: legacyExchangeDN
SMTP Address: SMTP Address
OWA version: OWA version
Mailbox server: Mailbox server

Exception type: Microsoft.Exchange.InfoWorker.Common.Availability.MissingArgumentException
Exception message: Element Number of MailboxArray is null.

Call stack
Microsoft.Exchange.Clients.Owa.Core.Utilities.ExecuteAvailabilityQuery(OwaContext owaContext, AvailabilityQuery query. Boolean expectFreeBusyResults, Boolean expectMergedFreeBusyResults, AvailabilityQueryResult& result)
Microsoft.Exchange.Clients.Owa.Core.Utilities.ExecuteAvailabilityQuery(OwaContext owaContext, AvailabilityQuery query. AvailabilityQueryResult& result)
Microsoft.Exchange.Clients.Owa.Basic.CalendarItemSchedulingTab.OnLoad(EventArgs e)
System.Web.UIControl.LoadRecursive()System.Web.UIPage.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)


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.