Requesting data from Microsoft Exchange Server

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To edit the registry to manually suppress the Cancel Request dialog box:
Start Registry Editor (Regedt32.exe).
Locate and click on the appropriate registry key listed below based on the method that was used to install Microsoft Outlook.
If the Installation Wizard was used to install Outlook:

HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\CancelRPC

If the Custom Installation Wizard was used to install Outlook:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\10.0\Outlook\CancelRPC

On the Edit menu, click Add Value, and then add the following registry value:
Value name: Disable
Data type: DWORD
Value data: 1

Quit Registry Editor.

Changing the "Cancel Request" Dialog Box Time-Out Value
You can also manually specify the amount of time that Outlook waits for a connection to the server before the Cancel Request dialog box is displayed. This policy setting overrides the Exchange service Seconds until server connection timeout setting, although it does not disable this setting in the user interface (UI). To edit the registry to modify the policy setting:
Start Registry Editor (Regedt32.exe).
Locate and click on the appropriate registry key listed below based on the method that was used to install Microsoft Outlook.
If the Installation Wizard was used to install Outlook:

HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\CancelRPC

If the Custom Installation Wizard was used to install Outlook:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\10.0\Outlook\CancelRPC

On the Edit menu, click Add Value, and then add the following registry value (in this example, the value is set to 50 seconds):
Value name: TimeToShowCancelDialog
Data type: DWORD
Value data: 50000 (the amount of time in milliseconds)

NOTE: Type the connection delay that you want to allow as a decimal number representing milliseconds.
Quit Registry Editor.
<<ref: http://support.microsoft.com/?kbid=293650



petes footnote

this part of the reg key (Office\10.0\) differs depending on your version of outlook :)

Petelongs answer will stop the dialog box from appearing, but that only cures the symptom, not the problem.  The problem is that the exchange server is making the clients wait for information.  This is a very broad problem that you will have to work down to the cause.

The first thing I would look for is on the exchange server, map the CPU usage and the Ram usage through the day and review.  Are you hitting 100% on either.  How much space is left on the server and how fast is it.  

Do the users get this at a sepcific time of day, or is it always.  If so what happens at that time of day.  
Does it happen to all users or just some?  What is different between groups that it is not happening to?
When did it start?  What changes where made to the NETWORK or server when it started?
Are the nic cards in the server new or old? How about the switch they connect to?

Once you narrow it down a little please post and I will work with you to solve this.

Please post the OS and specs of the Exchange server and any other information about your network that might be significant.  Also post what virus and/or spam protection you are using ON THE SERVER.

I'm waiting for a response from Back Office in regards to your above suggestion.  

Back Office is saying:  "We have already identified the problem with the ARP cache and Exchange cluster, the "requesting data"  is just a result of the that."

Thank you very much for your help.