Outlook: Unable to perform a Check Name or connect to an Exchange mailbox

When you start Outlook with a profile for an Exchange mailbox, you may receive the following error:

• Cached mode profile
  
  The file c:\documents and settings\username\local settings\application data\Microsoft\Outlook\outlook.ost cannot be accessed because it has been configured for use with a different mailbox.
  
• Online mode profile
  
  Microsoft Exchange is unavailable.
  

Also, when you try to create a new Outlook profile, you may receive one of the following errors:

Outlook cannot log on. Verify you are connected to the network and are using the proper server and mailbox name. The connection to the Microsoft Exchange is Unavailable. Outlook must be online or connected to complete this action.

This issue occurs when the HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders registry key does not contain all of the required data. Specifically, these problems occur if the AppData string value is missing from this registry key.

NOTE: The \User Shell Folders key also contains a string value called Local AppDatawhich is different from the value called AppData. The value that causes this problem (if it is missing) is the AppData value.

To resolve this issue, import the User Shell Folders registry key from a working Windows User Profile.

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

• Steps to perform on a working computer
  1. Start Registry Editor.
     
     In Windows 7, click Start , type regedit in the Search programs and files box, and then press Enter.
     
     In Windows Vista, click Start, type regedit in the Start Search box, and then press Enter.
     
     In Windows XP, click Start, click Run, type regedit, and then click OK.
     
  2. Locate and then select the following registry subkey:
     
     HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
     
  3. On the File menu, click Export.
  4. Specify the name of the .reg file and then click Save.
  5. Copy the .reg file to the computer exibiting this problem.
  6. Close Registry Editor.
• Steps to perform on the computer displaying the above error(s)
  1. Start Registry Editor.
     
     In Windows 7, click Start , type regedit in the Search programs and files box, and then press Enter.
     
     In Windows Vista, click Start, type regedit in the Start Search box, and then press Enter.
     
     In Windows XP, click Start, click Run, type regedit, and then click OK.
     
  2. On the File menu click Import.
  3. Locate and select the .reg file exported from the working computer.
  4. Click Open.
  5. Close Registry Editor.