Microsoft Knowledge Base Article 839862 contains the following summary and introduction:

SUMMARY

This article describes typical troubleshooting steps that you can use to determine the root cause for receiving the following message:

Outlook is retrieving data from the Microsoft Exchange Server <Server name>. You can cancel the request or minimize this message to the Windows taskbar until Outlook closes the message automatically.

INTRODUCTION

In versions of Microsoft Outlook that are earlier than Outlook 2002, Outlook periodically appears to stop responding (hang) when users send e-mail messages, receive e-mail messages, check appointments, or create appointments . When Outlook stops responding, users see an hourglass until Outlook has the information that it requires . The types of data that Outlook retrieves during this period include information in the user's mailbox, information in the user's public folders, free/busy information, and directory look-ups (check-name) . The server that Outlook queries for this information is either a Microsoft Exchange Server computer or a global catalog server . If the server name appears as a NetBIOS name, the data is being retrieved from an Exchange Server computer . If the server name appears as a fully qualified domain name (FQDN), the data is being retrieved from a global catalog server.

The remote procedure call (RPC) Cancel Request dialog box is a feature that was added in Microsoft Outlook 2002. With this feature, users can see the server that Outlook is accessing. Additionally, by using the Cancel Request dialog box, users can cancel the data retrieval.

When Outlook 2002 and later versions request data from an Exchange Server computer, Outlook calls a function that wraps the RPC to the server. This new wrapper is the Cancelable RPC wrapper. By default, the Cancelable RPC wrapper starts a timer and issues the RPC. When the RPC is complete, the wrapper closes the timer, cleans up, and quits. However, if the RPC for data takes more than 5 seconds to return the data, the wrapper produces the Cancel Request dialog box. The Cancel Request dialog box remains on the screen until the RPC is answered or until the user clicks Cancel . If the action that the user performs in Outlook causes multiple RPCs to be made, the user may receive a Cancel Request dialog box for each RPC.

Although the Cancel Request dialog box was intended to improve the user experience by providing server information when Outlook stopped responding, many users interpret this message as an error message and contact their help desk for more information, instead of understanding that the Cancel Request dialog box occurs as an ordinary part of Outlook and Exchange interoperation. On the fastest network with the best hardware and the best architecture, sometimes an RPC takes more than 5 seconds to obtain a response. If the Cancel Request dialog box appears only occasionally, 'extensive troubleshooting is not required and is not productive. However, if users receive the Cancel Request dialog box frequently and for extended periods, there may be a performance issue with one of the servers or a problem with the network. This article discusses troubleshooting steps that you can use to determine the root cause of frequent Cancel Request dialog boxes.

For more information about how to disable the Cancel Request dialog box feature or how to increase the time-out value if you experience frequent network congestion or other related issues, click the following article number to view the article in the Microsoft Knowledge Base:

293650 How to change the Cancel Request dialog box behavior in Outlook 2002