Problem solve Get help with specific problems with your technologies, process and projects.

Common Outlook DLL errors

Outlook will occasionally produce obscure DLL error messages. This article discusses a few of the more common ones and offers solutions.

Please let others know how useful this tip is via the rating scale at the end of it. Do you have a useful Exchange or Outlook tip, timesaver or workaround to share? Submit it to our tip contest and you could win a prize.


Outlook will occasionally produce obscure DLL error messages. In this article, I discuss a few of the more common ones and offer solutions.

"Outlook caused an invalid page fault in RICHED20.DLL"

This error message indicates that the RICHED20.DLL file is either corrupt or missing, and usually prohibits Outlook from launching. Alternatively, Outlook may start OK, but act up when you try to compose an e-mail. If this happens, the error message becomes: "Unable to load RICHED20.DLL. You may be out of memory, out of system resources, or missing a DLL file."

To resolve either error, search your system for the RICHED20.DLL file and rename it to RICHED20.OLD. Then, start Outlook and run the Detect and Repair option from the Help menu.

You can get more detailed information on troubleshooting this problem in KB article 825231.

"A recently installed program may cause Microsoft Office or other e-mail enabled programs to function improperly"

You may run into this problem if you install a MAPI-enabled program that uses an older version of MAPI32.DLL. In fact, I recently wrote an article on how to install Exchange System Manager on an XP workstation. After performing this process, several readers reported receiving this error.

Windows includes a utility called FIXMAPI.EXE that you can use to fix it. Microsoft recommends that you rename the MAPI32.DLL file to MAPI32.OLD prior to running the FIXMAPI.EXE program though, because there is potential for things to go awry. If something does go wrong, you can always delete MAPI32.DLL and then rename MAPI32.OLD back to MAPI32.DLL.

You can read more about this issue in KB article 813602.

"A system component, RPC, required by Outlook to connect to the e-mail server is not configured properly"

This does not specifically mention a DLL file, but it is DLL related. There are four different registry keys that must reference the RPCRT4.DLL file in order for RPC to function properly. If you receive the above notification, the registry is most likely configured incorrectly.

Important: Making incorrect modifications to the registry can destroy Windows and/or your applications. Therefore, create a full system backup before continuing.

Now, enter the REGEDIT command at the Run prompt to open the Registry Editor and navigate through the registry tree to: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols.

Verify that this key contains the following values: ncacn_np, ncacn_ip_tcp, ncadg_ip_udp, ncacn_http. Each of these registry keys should have the value RPCRT4.DLL associated with it.

If one of the values is missing, right click on the ClientProtocols container and select the New -> String Value command. Type the name of the missing value when prompted and press Enter. Then, right click on the value that you just created and select Modify. Finally, enter RPCRT4.DLL as the value data and click OK.

You can get more information about this fix in KB article 830914.

If you are experiencing a DLL error I have not covered in this article, I recommend consulting the Microsoft Knowledge Base.

About the author: Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Windows 2000 Server and IIS. Brien has served as CIO for a nationwide chain of hospitals and was once in charge of IT security for Fort Knox. As a freelance technical writer he has written for Microsoft, CNET, ZDNet, TechTarget, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal Web site at


When I saw the topic of this article, I was hoping to see the DLL error I receive every time I launch Outlook 2003 on my Windows XP machine. The error is:

The add-in "C:\Windows\system32\dhswp32.dll" could not be installed or loaded. This problem may be resolved by using the Detect and Repair on the Help menu.

I have done numerous searches on the Internet for this DLL and have come up empty. It doesn't seem to exist, and it isn't anywhere on my hard disk. If you have any idea where this error is coming from, I'm all ears. It doesn't seem to adversely affect the performance of my machine or the functionality of Outlook, but it's pretty annoying to see every time I launch Outlook.
—Paul E.


I had the same problem when upgrading Symantec Antivirus on a workstation. To resolve the problem we did the following -- close Outlook, navigate to HKLM\Software\Microsoft\Exchange\Client\Extensions and delete the value referencing the DLL. Then search for the fix extend.dat on your hard drive and delete it. Restart Outlook and the problem should be solved.
—Crash C.

Do you have comments on this tip? Let us know.

Dig Deeper on Outlook management