Microsoft Knowledge Base Article 839880 contains the following summary and introduction:

SUMMARY

You may experience RPC Endpoint Mapper errors when you use specific tools and utilities that are available in the Support folder of the Microsoft Windows Server CD-ROM, available as part of a Windows Server Resource Kit, or available on the Microsoft Web site. These errors can help you troubleshoot RPC Endpoint Mapper issues.

The symptoms that are described in this article do not represent every possible scenario that may result when RPC does not function correctly. RPC is used by several components in Windows Server 2003 and Windows 2000 Server, such as the File Replication Service (FRS), Active Directory Replication, Certificate services, DCOM, Microsoft Message Queuing (also known as MSMQ), and MAPI. Therefore, a variety of errors and symptoms may occur when RPC does not function correctly.

INTRODUCTION

This step-by-step article describes how to troubleshoot Remote Procedure Call (RPC) Endpoint Mapper errors in Windows Server 2003 and Windows 2000 Server by using tools and utilities that are available in the Support folder of the Windows Server 2003 or Windows 2000 Server CD-ROM or that are available as part of the Windows Server 2003 Resource Kit or the Windows 2000 Server Resource Kit . Remote Procedure Call is a protocol that is used by the Windows operating system . RPC provides an inter-process communication mechanism that allows a program running on one computer to run code on a remote system.

In certain situations, when you try to force Active Directory replication by using Active Directory Sites and Services, when you try to promote an additional domain controller by using the Dcpromo tool, or when you run netdom query fsmo from a command line, you may receive an error message that is similar to the following:
There are no more endpoints available from the endpoint mapper.
Other symptoms may include:
When you try to log on to the domain, you may receive an error message that is similar to the following: The system cannot log you on to this domain because the system's computer account in its primary domain is missing or the password on that account is incorrect.
You cannot open Group Policy snap-ins.
When you try to open Active Directory Administrative Tools, such as Active Directory Users and Computers or Active Directory Sites and Services, you may receive the following error message:
The specified domain either does not exist or could not be contacted.
You cannot browse the domain in Network Neighborhood.
You receive the following error message when you try to map drives or view resources on a remote server:
Access denied.
File Replication Service (FRS) may be slow or fail completely. For example, the Sysvol folder may fail to replicate between domain controllers. When this occurs, you may receive a message similar to the following in the Ntfrs_000<x>.log files:
RPC Unavailable
Microsoft Outlook may fail when connecting to a Microsoft Exchange server. When this occurs, you may receive username and password prompts when you open Outlook. When you enter valid credentials, you may receive an error message similar to the following:
Your logon information is incorrect
-OR-
Outlook could not logon.
Also, when you click Check Name while creating a new mail account in Outlook, you may receive an error similar to the following:
The name could not be resolved. The name could not be matched to a name in the address list.

Note If you use a network capture program, such as Network Monitor, to capture network traffic, the computer may not receive a response when it tries to establish an RPC session to another computer by using any port greater than 1024. The sending computer uses the Universal Unique Identifier (UUID) for the RPC Endpoint Mapper. The UUID for the RPC Endpoint Mapper is E1AF8308-5D1F-11C9-91A4-08002B14A0FA.