You cannot log on to an Exchange Server computer when you are running Outlook

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This article was previously published under Q268575
NOTE: The procedures in this article only apply if you have installed Outlook with the Corporate or Workgroup option. With this option, you can use Messaging Application Programming Interface (MAPI) services. To determine your installation type, click About Microsoft Outlook on the Help menu. If you have the Corporate or Workgroup installation, you see "Corporate or Workgroup".
When you attempt to connect to a Microsoft Exchange Server-based computer and you are running Microsoft Outlook on a Microsoft Windows 2000 Professional-based or a Microsoft Windows XP Professional-based computer, you may receive any of the following error messages:
The Microsoft Exchange address book was unable to log on to the Microsoft Exchange server computer. Contact your system administrator if the problem persists.
Your logon information is incorrect.
Outlook could not logon.

Cause 1

This behavior occurs because the Transmission Control Protocol/Internet Protocol (TCP/IP) stack is initialized incorrectly.

Cause 2

This behavior can also be caused if the following registry key is corrupted or missing:

Resolution 1

To resolve this behavior, uninstall and then reinstall TCP/IP from the Windows 2000-based computer. For more information about how to uninstall and install TCP/IP, see the "More Information" section of this article.

NOTE: Remove TCP/IP as your last step after you have tried all basic troubleshooting steps.

Resolution 2

To replace this registry key, export the key from another computer, and then import it on the affected computer.
For more information about how to troubleshoot before you remove TCP/IP, click the following article numbers to view the articles in the Microsoft Knowledge Base:
195795 How to troubleshoot Outlook 2000 configuration problems
258495 Troubleshooting client connectivity issues by using command-line utilities
167260 How to use RPCPing to Test RPC communication
174701 Troubleshooting RPC problems for Exchange clients

How to Uninstall TCP/IP

  1. Log on as the local administrator.
  2. Close all open programs, and then disable any anti virus program.
  3. Right-click My Network Places on your desktop, and then click Properties.
  4. Right-click Local Area Connection, and then click Properties.
  5. Click Internet Protocol (TCP/IP), and then click Uninstall.
  6. You receive the prompt to uninstall TCP/IP, click Yes.
Your computer restarts.

How to Reinstall TCP/IP

  1. Log on as the local administrator
  2. Right-click My Network Places on your desktop, and then click Properties.
  3. Right-click Local Area Connection, and then click Properties.
  4. Click Install, and then click Protocols.
  5. Click Add.
  6. Click Internet Protocol (TCP/IP), and then click OK.
  7. Click Close in the Local Area Connection Properties dialog box, and then restart your computer.
  8. Log on to the network, and then verify that Outlook resolves the Exchange Server name and the mailbox name.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
255843 Unable to log on to Exchange Server from a Windows 2000 or Windows XP client
ol2007 ol2003 OL2K check name

Article ID: 268575 - Last Review: 01/27/2007 17:43:10 - Revision: 3.1

Microsoft Office Outlook 2007, Microsoft Office Outlook 2003, Microsoft Outlook 2002 Standard Edition, Microsoft Outlook 2000 Standard Edition, Microsoft Outlook 98 Standard Edition, Microsoft Outlook 97 Standard Edition

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