Microsoft Outlook 2010 does not prompt for credentials if one of the following conditions is true:
You start Outlook 2010 as an initial application in a remote desktop (RDP) session.
You start Outlook 2010 as a published application in Citrix Zen.
To resolve this issue, apply the following update:
2596996 Description of the Office 2010 hotfix package (x86 Mso-x-none.msp, x64 Mso-x-none.msp): December 13, 2011
Registry key information
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
After you install the hotfix package, follow these steps to enable the hotfix: