You receive error message and are continuously prompted for your Windows NT domain credentials in Outlook 2000, Outlook 2002, or Outlook 2007

When you start Microsoft Outlook, you may receive one of the following error messages: When you start Outlook against your Microsoft Exchange Server mailbox, you receive a prompt for your Windows domain credentials multiple times. After you receive several prompts, you finally gain access to the server. However, you may receive more prompts during the session.

This behavior occurs because the system registry may be missing one or more values in the following registry key: The following values are the core required values for Windows XP or Windows 2000:


The following values are the core required values for Windows 98:


Following the system's protocol binding order, you receive a prompt for credentials on each missing value until a value that matches the next protocol in the binding order is reached.

Use one of the following methods to resolve this behavior.

Method 1

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:

Import a valid registry key from a computer that is working correctly. To do this:

1. Start Registry Editor (Regedt32.exe).
2. Locate and then click the following key in the registry:
   KEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols
3. Click the ClientProtocols key.
4. On the File menu, click Export.
5. Save the file with a .reg or a .txt extension in the event you need to send the file by using Outlook. You must save and rename the attachment to a .reg extension to import the key.
6. Quit Registry Editor.
7. Rename the file that you just exported from a .txt file extension to a .reg extension, and then copy it to a folder on your computer.
8. Start Registry Editor (Regedt32.exe).
9. Locate and then click the following key in the registry:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols
10. Select the ClientProtocols folder, click File, and then click Import.
11. Select the .reg file that you saved, and then click Open.
12. Quit Registry Editor.
13. Quit and then restart Outlook 2002.

Method 2

Use Registry Editor to manually create the missing values. To do this:

1. Start Registry Editor (Regedt32.exe).
2. Locate and then click the following key in the registry:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols
3. Click Edit, click New, and then click String Value.
4. Edit the new string value with the name and data information that is in the table in the "Cause" section of this article.
5. Repeat steps 3 and 4 for each missing value.
6. Quit Registry Editor.