You receive error message and are continuously prompted for your Windows NT domain credentials in Outlook 2000 or in Outlook 2002 (321652)

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SYMPTOMS

When you start Microsoft Outlook, you may receive one of the following error messages:

Your logon information was incorrect. Check your username and domain, then type your password again. If your account is new or if your administrator requested a password change you need to click Change Password then logon with your new password.

-or-

The logon credentials supplied were incorrect. Make sure your username and domain are correct, then type your password again.

When you start Outlook against your Microsoft Exchange Server mailbox, you receive a prompt for your Windows NT 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.

CAUSE

This behavior occurs because the system registry may be missing one or more values in the following registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols

The following values are the core required values for Windows XP or Windows 2000:

Name	Type	Data
(Default)	REG_SZ	(value not set)
ncacn_http	REG_SZ	Rpcrt4.dll
ncacn_ip_tcp	REG_SZ	Rpcrt4.dll
ncacn_np	REG_SZ	Rpcrt4.dll
ncacn_nb_tcp	REG_SZ	Rpcrt4.dll
ncadg_ip_udp	REG_SZ	Rpcrt4.dll

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

Name	Type	Data
(Default)	REG_SZ	(value not set)
ncacn_np	REG_SZ	Rpcltc1.dll
ncalrpc	REG_SZ
ncadg_ip_udp	REG_SZ	Rpcltc3.dll
ncacn_http	REG_SZ	Rpcltccm.dll

The following values are the core required values for Windows NT 4.0:

Name	Type	Data
(Default)	REG_SZ	(value not set)
ncacn_np	REG_SZ	Rpcltc1.dll
ncalrpc	REG_SZ
ncadg_ip_udp	REG_SZ	RpcLtCcm.dll
ncadg_ip_udp	REG_SZ	RpcLtCcm.dll
ncacn_nb_tcp	REG_SZ	RpcLtCcm.dll
ncacn_http	REG_SZ	RpcLtCcm.dll

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.

RESOLUTION

Use one of the following methods to resolve this behavior.

Method 1

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

Start Registry Editor (Regedt32.exe).
Locate and then click the following key in the registry:
KEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols
Click the ClientProtocols key.
On the File menu, click Export.
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.
Quit Registry Editor.
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.
Start Registry Editor (Regedt32.exe).
Locate and then click the following key in the registry:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols
Select the ClientProtocols folder, click File, and then click Import.
Select the .reg file that you saved, and then click Open.
Quit Registry Editor.
Quit and then restart Outlook 2002.

Method 2

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

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