How to Fix Outlook RPC Error

An RPC error can occur when the registry values that connect Outlook to your Exchange Server become corrupted. Outlook communicates with Exchange Server using Remote Procedure Calls (RPCs). A procedure is a small piece of code designed to do one particular thing. The programs you run on your computer may be made up of hundreds, even thousands of procedures.

In most desktop programs, all the procedures will run on your computer, but for some applications procedures may be run on a remote computer. Outlook, for example, has many procedures that run on your computer, but it communicates with Exchange Server by executing remote procedures.

Checking the Registry

The good news is that the Outlook RPC error can often be fixed. The bad news is you need to edit the Registry by hand to fix it. The Registry is a database used by Windows to keep track of information used to run the different applications you have installed, as well as Windows itself.

The first thing to do is to open RegEdit.exe, a built-in Windows program for editing the Registry.

WARNING: Changing or deleting entries in the Registry can make it so that Windows does not run. Be very careful and change only exactly what you need to change to fix this bug

You can run regedit.exe by typing it into the Windows Address bar. If that isn't visible, you can choose Run from the Start menu (in Windows XP) or type "regedit.exe" directly into the program search edit box on the Start Menu (in Vista).

In RegEdit, navigate through the folders on the left to the following location:

• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols
On the right side you should see four entries:
• ncacn_np
• ncacn_tcp
• ncacn_udp
• ncacn_http.

In the data column next to each entry, it should say "rpcrt4.dll". If there are not four entries or any of the data doesn't reference the rpcrt4.dll, then you may have found your problem.

Adding an Entry
To add a missing entry:

• Right click on Client Protocols on the left side.
• Point to New, and then select String Value from the context menu.

Modifying an Entry Value
To change the value for an entry:

• Double click on the entry
• In the Edit String dialog window enter "rpcrt4.dll" (no quotes), then press the OK button.

When you have all four entries correctly installed, close RegEdit, and run Outlook to see if this fixed the problem.